Molecular Simulation Ontology

An enhanced sampling algorithm is a computational procedure that modifies a standard simulation to accelerate the exploration of a molecule's possible shapes or to observe rare events. These algorithms are designed to overcome the high energy barriers that can trap a simulation in a single state for a long time. For experts, this category includes the specific algorithms that implement methods like metadynamics, replica exchange, or steered molecular dynamics. (UNVERIFIED)

• well-tempered metadynamics algorithm ^c
• steered molecular dynamics algorithm ^c
• metropolis Monte Carlo ^c
• replica exchange algorithm ^c
• Wang-Landau algorithm ^c
• adaptive biasing force algorithm ^c
• multiple-walkers algorithm ^c

A simulation method is a computational technique that mimics how a system changes over time. As a type of computational method, it involves numerically integrating equations of motion to generate a trajectory that describes the system's dynamic evolution, such as in molecular dynamics or enhanced sampling. The choice of simulation method dictates the physical laws and algorithms used to propagate the system's state, as controlled by parameters in the main simulation input file. This is referred to in log files and inputs with keywords like "integrator," "dynamics," "nsteps," and "dt." (UNVERIFIED)

• computational method ^c
• empirical method ^c

• multiscale simulation method ^c
• monte carlo simulation ^c
• simulation type ^c
• QM/MM simulation ^c
• restrained simulation method ^c
• molecular dynamics ^c

A collective variable is a simplified coordinate that helps describe a complex process in a simulation, such as the distance between two proteins as they bind. Instead of tracking thousands of atomic coordinates, a collective variable reduces the system's motion to one or a few key parameters that capture the essence of the event. These variables are frequently used in enhanced sampling methods to focus computational effort on exploring a specific conformational change or reaction pathway. (UNVERIFIED)

• torsion collective variable ^c
• reaction coordinate ^c
• distance collective variable ^c
• angle collective variable ^c
• center of mass angle collective variable ^c
• handedness collective variable ^c
• number of bonds collective variable ^c
• multi-RMSD collective variable ^c
• radius of gyration collective variable ^c

This is a specialized file format used in constant pH simulations to define the properties of amino acids that can change their protonation state. The library file contains the topologies for both the protonated and deprotonated forms of a titratable residue, such as aspartic acid. This format allows the simulation engine to dynamically switch between the different residue states during the simulation to model pH-dependent effects correctly. (UNVERIFIED)

This likely refers to GAMESS-US (General Atomic and Molecular Electronic Structure System), a widely used, freely available quantum chemistry software package. It provides a broad range of quantum mechanical methods (HF, DFT, MP2, CCSD, MCSCF) and features for geometry optimization, vibrational analysis, property calculation, and QM/MM simulations. GAMESS-US is extensively used in computational chemistry research and education for electronic structure calculations relevant to biomolecular systems. (UNVERIFIED) (If GAMESS-UK was intended, see previous definition)

An approximate method for handling long-range electrostatic interactions where direct interactions are calculated only up to a certain cutoff distance. The effect of charges beyond the cutoff is approximated by embedding the cutoff sphere within a continuous dielectric medium representing the solvent. While computationally cheaper than PME, its accuracy depends on the system and parameters chosen (UNVERIFIED).

Non-equilibrium molecular dynamics (NEMD) is a class of simulation techniques where the system is actively driven away from thermodynamic equilibrium by the application of external forces or constraints. Instead of observing natural fluctuations, researchers use this method to study how the system responds to stress, such as mechanical pulling, shearing flow, or thermal gradients. For experts, these simulations are governed by non-Hamiltonian equations of motion or time-dependent biases and are fundamental for calculating transport coefficients or recovering equilibrium free energies using fluctuation theorems. (UNVERIFIED)

A unit of energy per amount of substance per area, commonly used in molecular dynamics simulations for expressing force constants and restraint weights.

The 3D Reference Interaction Site Model (3D-RISM) is a sophisticated analysis method based on statistical mechanics that calculates the three-dimensional distribution of solvent molecules around a solute. It is an implicit solvent model that provides a detailed, atomistic picture of the solvation structure without the computational cost of simulating explicit solvent molecules. For experts, 3D-RISM is a powerful method for calculating solvation free energies and for predicting the location of tightly bound water molecules. (UNVERIFIED)

A simulation technique that allows a user to visualize and physically manipulate a running molecular simulation in real-time. Through a specialized interface or haptic device, the user applies external forces to specific atoms while the simulation engine calculates the system's response on the fly. For experts, IMD uses a client-server architecture where the visualization client sends force vectors to the simulation server, which integrates these as time-dependent external potentials, useful for guiding docking or unfolding pathways. (UNVERIFIED)

This is a utility script from the edgembar software package used to process the output from a specific type of free energy calculation. It likely extracts the necessary energy data from simulations of the "bookend" or reference states in a large alchemical network. This data preparation is a required step before the main edgembar program can combine all the results to calculate the final relative free energies. (UNVERIFIED)

An adaptive Poisson-Boltzmann solver is a sophisticated algorithm for calculating the electrostatic properties of a molecule in a solvent. It solves the Poisson-Boltzmann equation on a grid that automatically becomes finer in regions where the electrostatic potential is changing rapidly, such as near the charged atoms of the molecule. This adaptive approach allows for a highly accurate calculation of electrostatic energies with greater computational efficiency than using a uniformly fine grid everywhere. (UNVERIFIED)

A running average calculation is a statistical analysis technique used to smooth out short-term fluctuations in time-series data and highlight longer-term trends. It is calculated by averaging a property over a sliding time window as the simulation progresses. For simulation experts, monitoring the running average of properties like the total energy or temperature is a standard method for assessing whether a simulation has reached a stable equilibrium. (UNVERIFIED)

• This can also be a coordinate format from Tinker package as well.

• A file format used by the TINKER simulation package to store the trajectory of a molecular system. It archives the atomic coordinates from different snapshots of a simulation in a single file for later analysis. This is the standard trajectory output for TINKER simulations. (UNVERIFIED)

The Optimized Potentials for Liquid Simulations force field family, developed by William L. Jorgensen and colleagues. This family encompasses several versions (e.g., OPLS-AA, OPLS-UA) designed for simulating organic liquids, proteins, and other biomolecules. A key focus during parameterization is accurately reproducing experimental properties of liquids, like density and heat of vaporization. (UNVERIFIED)

The simplest simulation box shape, defined by three mutually perpendicular axes (orthogonal box). If all edge lengths are equal, it is cubic; otherwise, it is rectangular (also called orthorhombic or cuboid). While straightforward to implement and visualize, cubic boxes can be inefficient for solvating non-cubic solutes, often requiring significantly more solvent molecules than more spherically approximating shapes like the truncated octahedron to achieve the same minimum distance between periodic images. (UNVERIFIED)

A link atom is a "dummy" atom, usually a hydrogen, used in hybrid QM/MM simulations to properly cap the broken chemical bond at the boundary between the high-accuracy and low-accuracy regions. When a covalent bond is cut between the quantum mechanics (QM) and molecular mechanics (MM) regions, the link atom is introduced along this bond to saturate the valency of the QM atom, preventing unrealistic electronic effects. The proper placement and treatment of these link atoms is one of the most critical aspects of a QM/MM simulation, as it directly affects the accuracy of the calculated energies and forces at the interface. (UNVERIFIED)

A statistical ensemble representing completely isolated systems, where the number of particles (N), the system volume (V), and the total energy (E) are all held constant; hence often called the NVE ensemble. There is no exchange of energy or particles with the surroundings. Simulations performed in the NVE ensemble directly follow Newtonian laws of motion (integrating Hamilton's equations), and conservation of total energy serves as a key check of simulation stability and accuracy, but it's less commonly used for equilibrium sampling compared to NVT or NPT as temperature can fluctuate. (UNVERIFIED)

Protein-peptide docking analysis is a computational method specifically designed to predict the three-dimensional structure of a complex formed between a protein receptor and a short peptide ligand. Unlike small molecule docking, these algorithms must explicitly account for the high flexibility and numerous degrees of freedom found in the peptide's backbone and side chains. This analysis is essential for understanding cell signaling pathways mediated by peptide interactions and for designing peptide-based therapeutic agents. (UNVERIFIED)

A specific protein force field parameter set from the AMBER family (ff), released around 2014, with optimizations primarily for side-chain (S) and backbone (B) torsion angles compared to earlier versions like ff99SB. It was widely adopted for its improved accuracy in representing protein secondary structure and dynamics. It is an all-atom force field. (UNVERIFIED)

A form of electronic structure analysis that investigates the molecular orbitals (MOs) of a system, which represent the energy levels and spatial distributions of electrons within the molecule based on quantum mechanics. Common analyses include visualizing frontier orbitals (HOMO, LUMO), examining orbital compositions (e.g., atomic orbital contributions), analyzing orbital energies for insights into ionization potential or electron affinity, and relating MOs to chemical bonding, reactivity, and electronic transitions. It helps rationalize chemical behavior based on electron distribution in orbitals. (UNVERIFIED)

A component of the system's energy that describes short-range non-covalent interactions, including both Pauli repulsion and attractive dispersion forces. It is typically calculated using a Lennard-Jones potential and is fundamental for modeling molecular size, shape, and packing. The stability of the Van der Waals energy is a key indicator of proper system density and packing during equilibration. This value is reported in simulation outputs as E_vdw, VDWAALS, VDW, or Lennard-Jones. (UNVERIFIED)

MM/PBSA is an endpoint method used to estimate binding free energies by combining molecular mechanics (MM) energy calculations with continuum solvation models. It calculates the free energy change by summing the change in MM energy in vacuum, the change in polar solvation free energy (calculated using Poisson-Boltzmann electrostatics), and the change in nonpolar solvation free energy (estimated from solvent-accessible surface area). This approach analyzes snapshots from molecular dynamics simulations of the bound and unbound states. (UNVERIFIED)

• hybrid solvent MM-PBSA analysis ^c
• trajectory approach analysis ^c
• active site focusing analysis ^c

A base pair parameter that quantifies the translational displacement of one base relative to the other along their short axis, within the plane of the base pair. A non-zero shear indicates a lateral sliding of the bases relative to their standard Watson-Crick hydrogen bonding positions. This is a standard output of nucleic acid analysis programs. (UNVERIFIED)

A solvation model that approximates the average effect of the solvent environment without explicitly representing individual solvent molecules. Instead, the solvent is treated as a continuous medium characterized by macroscopic properties, primarily its dielectric constant (ϵ) to account for electrostatic screening, and sometimes surface tension to account for nonpolar effects like cavity formation. Common examples include Generalized Born (GB) models and methods based on solving the Poisson-Boltzmann (PB) equation, often combined with a surface area term (SASA); these significantly reduce computational cost compared to explicit solvent. (UNVERIFIED)

• generalized Born surface area ^c
• generalized Born ^c
• generalized Born implicit solvent model ^c
• Poisson-Boltzmann model ^c
• Poisson-Boltzmann surface area ^c
• machine-learned solvent excluded surface model ^c

The atomic scattering factor is a measure of how strongly a single atom scatters waves, such as X-rays, which is a key piece of information for determining molecular structures from experiments. This factor depends on the number of electrons an atom has and the angle at which the X-rays are scattered. It is a fundamental component used in crystallographic refinement programs to calculate the theoretical diffraction pattern from a molecular model for comparison with experimental data. (UNVERIFIED)

Spectroscopy is the study of how matter interacts with energy, particularly electromagnetic radiation like light. By analyzing how energy is absorbed, emitted, or scattered by a substance, we can learn about its atomic and molecular structure, composition, and dynamics. It serves as a fundamental set of tools for observing the properties of molecules. (UNVERIFIED)

• magnetic spectroscopy ^c
• vibrational spectroscopy ^c
• fluoroscence spectroscopy ^c
• specialized techniques ^c
• electronic spectroscopy ^c
• rotational spectroscopy ^c

The am1bcc program is a utility in the AmberTools suite that calculates atomic partial charges for organic molecules using the AM1-BCC method. It first performs a fast, approximate quantum mechanical calculation (AM1) and then applies a set of empirical "bond charge corrections" (BCC) to improve the charges. This two-step procedure provides a rapid and automated way to generate good-quality charges for drug-like molecules that are compatible with the GAFF force field. (UNVERIFIED)

In NWChem, topology information for molecular dynamics or QM/MM calculations is typically defined within the input file (.nw) using specific directives like TOPOLOGY. This section defines atom types, charges, and connectivity (bonds, angles, etc.) for the molecular system. Associated force field parameters are usually specified separately using directives like PARAMETERS. (UNVERIFIED)

The GAL17 force field is a specific material force field designed for the simulation of zeolites, which are porous crystalline materials. It includes parameters to model the aluminosilicate framework and its interactions with various guest molecules. For researchers in catalysis and materials science, the GAL17 force field provides a specialized tool for studying adsorption and diffusion processes within zeolite structures. (UNVERIFIED)

The aug-cc-pVDZ basis set is the Double-Zeta correlation-consistent basis (cc-pVDZ) augmented with a set of diffuse functions (one for each angular momentum in the valence set). These spatially extended diffuse functions are crucial for accurately describing systems with loosely bound electrons, such as anions, electronically excited states, and molecules involved in weak intermolecular interactions (e.g., van der Waals, hydrogen bonding). (UNVERIFIED)

A computational tool designed to identify and characterize pathways, channels, or tunnels within the structure of a macromolecule, typically a protein enzyme. These tunnels often connect a buried active site to the protein surface and are important for ligand entry/egress, solvent access, or product release. Tools like CAVER use geometric algorithms to find voids and pathways within the protein structure based on atomic coordinates. (UNVERIFIED)

• CHAP ^c
• CAVER ^c
• MOLE ^c
• HOLE ^c

A data format that stores the numerical coefficients and empirical rules defining the potential energy function of a molecular mechanics force field. It contains the specific values needed to calculate interactions between atom types, including equilibrium lengths and force constants for bonded terms (bonds, angles, dihedrals), as well as Lennard-Jones parameters and partial charges for non-bonded terms. For experts, these files (such as AMBER .dat/.frcmod or CHARMM .par) supply the fundamental physical constants required by the simulation engine to compute interatomic forces, and are kept strictly distinct from the molecular coordinates or run control settings. (UNVERIFIED)

• CHARMM par format ^c
• ReaxFF force field format ^c
• AMBER force field parameter format ^c
• frcmod format ^c
• DFTB parameter format ^c

A QM/MM region selection algorithm is a procedure used in adaptive QM/MM simulations to automatically decide which atoms should be included in the high-accuracy quantum mechanics (QM) region. This algorithm dynamically updates the QM/MM boundary during the simulation based on predefined rules, such as the distance of atoms from a reaction center. For experts, these algorithms are the core of adaptive methods that allow the QM region to follow the chemical action. (UNVERIFIED)

A well-defined sequence of steps or rules designed to perform a specific task or solve a particular problem. In computational science, algorithms provide the precise instructions for a computer to follow to achieve a desired outcome, such as simulating molecular motion or analyzing data. They are the fundamental building blocks of computational methods used in biomolecular simulation and analysis.

• enhanced sampling algorithm ^c
• optimization algorithm ^c
• minimum image convention ^c
• constraint algorithm ^c
• clustering algorithm ^c
• optimal transformation path algorithm ^c
• random number generator algorithm ^c
• analysis algorithm ^c
• simulation control algorithm ^c
• numerical integration algorithm ^c
• similarity calculation algorithm ^c
• quantum mechanics algorithm ^c
• numerical solver algorithm ^c
• trajectory analysis algorithm (deprecated) ^c

Generally refers to algorithms that operate based on proximity, often used in classification, clustering, or search problems. In pathfinding or optimization, a simple nearest neighbor approach might involve iteratively moving to the closest unvisited node, which is a heuristic that does not guarantee finding the globally optimal path (e.g., in the Traveling Salesperson Problem). It can also refer to K-Nearest Neighbors (KNN) classification/regression (UNVERIFIED).

An object-oriented quantum chemistry software package focused on developing and implementing novel electronic structure theories, particularly methods for electron correlation and response properties (e.g., for spectroscopy). It serves both as a research platform for method development and an application for advanced QM calculations. It provides a modern framework for tackling challenging quantum chemical problems. (UNVERIFIED)

A generic name for a text-based file format that stores the Cartesian (x, y, z) coordinates of atoms in a molecular system. The specific layout can vary, as multiple simulation packages like CHARMM and Amber have their own distinct versions of a ".crd" file. Due to its ambiguity, it is often necessary to specify which software's CRD format is being used. (UNVERIFIED)

• CHARMM crd format ^c
• AMBER crd format ^c
• CHARMM cor format ^c
• MPDyn crd format ^c

An analytical (non-iterative) constraint algorithm specifically designed for rigid water models like TIP3P or SPC/E, where both bond lengths and the bond angle are fixed. Because the geometry is simple and fixed, the constraint equations for a water molecule can be solved analytically, making SETTLE significantly faster than iterative methods like SHAKE for constraining water. It is highly efficient for simulations with explicit water (UNVERIFIED).

A torsion collective variable is a coordinate that tracks the value of a specific dihedral angle, which describes the rotation around a chemical bond. These variables are fundamental for describing the detailed three-dimensional shape of a flexible molecule. They are often used in enhanced sampling simulations to accelerate the rotation of protein side chains or to explore different backbone conformations. (UNVERIFIED)

• paired dihedral collective variable ^c
• sum of sines of dihedrals collective variable ^c
• sum of cosines of dihedrals collective variable ^c
• pattern dihedral collective variable ^c
• center of mass torsion collective variable ^c

A type of structural analysis focused on calculating and interpreting the potential energy associated with specific molecular structures or conformations obtained from simulations or modeling. This includes calculating single point energies, comparing energies of different conformers, or decomposing the total energy into contributing components. It helps assess the stability and likelihood of different structures. (UNVERIFIED)

• single point energy analysis ^c
• high accuracy energies analysis ^c
• binding energy analysis ^c
• energy decomposition analysis ^c

This is an advanced algorithm used to accelerate the convergence of complex, iterative calculations in quantum chemistry. It works by using information from previous steps to intelligently guess a better solution for the next step. For experts, this solver is a variant of the DIIS (Direct Inversion in the Iterative Subspace) algorithm, which is essential for efficiently finding a stable electronic wavefunction in a Self-Consistent Field (SCF) procedure. (UNVERIFIED)

A nucleic acid system is a molecular simulation system where the main molecule of interest is a single nucleic acid molecule, such as a DNA duplex or a folded RNA. These simulations are typically performed in a box of water and ions to study the intrinsic structure, flexibility, and conformational dynamics of the nucleic acid. For experts, these simulations are fundamental for understanding the physical properties of our genetic material. (UNVERIFIED)

• DNA system ^c
• RNA system ^c

The aug-pc-2 basis set augments the polarization consistent basis set pc-2 with diffuse functions ('aug-'). The pc-2 level generally corresponds to polarized triple-zeta (TZP) quality, optimized for systematic convergence. Aug-pc-2 therefore provides TZP quality description along with diffuse functions needed for anions, interactions, polarizabilities, etc., within the pc-n convergence framework. (UNVERIFIED)

A planned process that provides a reference to an individual entity shared by a group of subscribers to refer to that individual entity.

The file for storing pre-calculated pairwise distances does not have a single, mandatory extension, but a common convention exists. The recommended format is a binary file, for which the conventional extension is .cmatrix. (UNVERIFIED)

MP4 stands for fourth-order Møller-Plesset perturbation theory, providing a higher level of electron correlation treatment by including energy contributions from single, double, triple, and quadruple excitations relative to the Hartree-Fock reference (often denoted MP4(SDTQ)). The inclusion of triple excitations, even if approximated, is particularly important for achieving high accuracy for many chemical systems. MP4 offers significantly better accuracy than MP2 but at a substantially higher computational cost. (UNVERIFIED)

A water model force field is a set of parameters specifically designed to simulate the behavior of water molecules, which are the most common solvent in biological systems. Different models vary in their complexity, such as the number of interaction sites used to represent a single water molecule, and are optimized to reproduce different experimental properties of liquid water. The choice of water model is a critical decision that can significantly impact the accuracy of a biomolecular simulation. (UNVERIFIED)

• TIP4P/Ice ^c
• SPC ^c
• TIP4P/2005 ^c
• SPCFW ^c
• TIP5P ^c
• TIP3P ^c
• TIP6P ^c
• TIP3PFW ^c
• TIP4P ^c
• WatFour (WT4) coarse-grained ^c
• OPC3-pol ^c
• SPC/E ^c
• polarizable water ^c
• SPC flexible ^c
• SPC/E-b ^c
• TIP3P-FB ^c
• TIP4P-Ew ^c
• OPC3 ^c

A realizable entity the manifestation of which brings about some result or end that is not essential to a continuant in virtue of the kind of thing that it is but that can be served or participated in by that kind of continuant in some kinds of natural, social or institutional contexts.

The shape Tanimoto score is a quantitative metric used to calculate the three-dimensional geometric similarity between the volumes of two aligned molecules. It is defined as the volume of the intersection of the two molecular shapes divided by the volume of their union, resulting in a value between 0 and 1. For computational chemists, this score is a fundamental tool in virtual screening for identifying non-identical molecular scaffolds that can fit into the same protein binding pocket. (UNVERIFIED)

Principal Component Analysis (PCA) is a statistical dimensionality reduction technique that identifies the principal components – orthogonal directions along which the variance in a dataset is maximized. By projecting the data onto the first few principal components, which capture the largest amount of variance, PCA reduces dimensionality while preserving the most significant patterns of variation. In simulations, it's often used to identify dominant collective motions from atomic trajectories. (UNVERIFIED)

The dimer method is a specific algorithm used to find transition state structures on a potential energy surface. It works by optimizing a "dimer," which consists of two closely spaced copies of the molecular structure, to find the direction of lowest energy curvature. The dimer is then moved "uphill" along this direction to converge on the saddle point, making it an effective method that only requires first derivatives (forces). (UNVERIFIED)

MP2 stands for second-order Møller-Plesset perturbation theory, representing the first and computationally least expensive level beyond Hartree-Fock that incorporates electron correlation effects. It calculates the second-order energy correction based on double excitations from the Hartree-Fock reference determinant. MP2 often provides a significant improvement in accuracy over Hartree-Fock for molecular geometries, interaction energies, and reaction energies, making it a very popular baseline correlation method. (UNVERIFIED)

An SCF parameter that controls the Direct Inversion in the Iterative Subspace (DIIS) algorithm, which is used to accelerate the convergence of the SCF procedure. These parameters define the size of the subspace and the number of attempts for the DIIS extrapolation. The DIIS parameter settings are crucial for the efficient convergence of many QM calculations. These are often set in a specific diis section of the input file. (UNVERIFIED)

• DIIS attempts ^c
• DIIS matrices ^c

The Multistate Bennett Acceptance Ratio (MBAR) is a statistically optimal method for analyzing data from multiple simulations performed at different thermodynamic states (e.g., different temperatures, or with different biasing potentials like in umbrella sampling). It efficiently combines all the collected data to calculate free energy differences between any pair of the simulated states and to compute equilibrium expectation values. MBAR generalizes the two-state BAR method. (UNVERIFIED)

An information content entity is an abstract concept representing any piece of data, information, or knowledge that can be identified and described. In the context of simulations, it refers to the abstract data itself, such as the concept of a molecular structure or a simulation parameter set, separate from the specific file format used to store it. This distinction helps in organizing and standardizing the description of simulation data and metadata. (UNVERIFIED)

• process output ^c
• process specification ^c
• molecular system specification ^c

• Distinct from the object property MOLSIM_001036. Modeled here as a Class (the variable itself).

• A simplified variable used to track the progress of a chemical reaction or a complex structural change. It reduces the motion of thousands of atoms into a single parameter that describes the transition from a starting state to a final state. For experts, while theoretically the minimum energy path on the free energy landscape, in practice, it is approximated by collective variables (like distances or RMSD) used in enhanced sampling methods like Umbrella Sampling. (UNVERIFIED)

An empirical metal center parameterization is a method for deriving force field parameters for a metal ion and its coordination site by fitting them to reproduce experimental data. This can include data such as crystal structures, vibrational frequencies, or binding energies for a set of known metal complexes. For experts, this approach is often necessary for metal ions because standard, general-purpose parameterization methods can fail to capture their complex electronic and bonding behavior. (UNVERIFIED)

The freely available component of the AMBER software package, containing numerous programs and utilities for biomolecular simulation tasks excluding the main high-performance simulation engine (pmemd). AmberTools includes programs for system setup (tleap), trajectory analysis (cpptraj), structure preparation (antechamber), energy minimization (sander), basic MD simulation (sander), QM calculations (sqm), free energy analysis (MMPBSA.py), and many others. It provides the essential infrastructure for preparing, analyzing, and modeling simulations run with AMBER or other programs. (UNVERIFIED)

A simulation box shape consisting of a hexagonal base extruded along a perpendicular axis. This shape is sometimes used for systems with inherent one-dimensional periodicity or symmetry, such as fibers (like DNA) or layered systems, where periodic boundary conditions are naturally applied across the hexagonal faces and along the prism axis. Its use is less common than cubic or truncated octahedral boxes for general globular protein simulations. (UNVERIFIED)

This is a sophisticated method for describing a molecule's charge distribution that goes beyond simple point charges on atoms, using more complex shapes to represent the electric field. A RESP permanent multipole charge model is a charge fitting procedure that assigns not only a point charge (monopole) to each atom but also higher-order multipoles like dipoles and quadrupoles. This model is a key component of advanced polarizable force fields that aim for a more detailed and physically accurate representation of intermolecular interactions. (UNVERIFIED)

placeAV.py is a utility script used to convert the predicted solvent binding sites from a Placevent analysis into explicit atomic coordinates. It reads the centers of high-density solvent regions determined by the analysis and places dummy atoms or water molecules at those specific locations within a structure file. This tool allows researchers to visualize potential hydration sites or use them as defined starting positions for explicit solvent molecules in subsequent simulations. (UNVERIFIED)

Volume is a thermodynamic property that represents the three-dimensional size of the periodic simulation box containing the molecular system. In simulations run at constant pressure, this value fluctuates as the barostat adjusts the box dimensions to maintain the target pressure. For experts, the average volume is a primary output used to determine the equilibrium density of the system, a key property for validating the simulation model. (UNVERIFIED)

A visualization method is a technique used to create a graphical representation of molecular data, allowing scientists to see and interact with their results. This includes generating 3D images of molecules, animating simulation trajectories, or plotting data in the form of 2D graphs. For researchers, visualization is an indispensable method for understanding complex structural information and communicating findings. (UNVERIFIED)

• worm plot visualization analysis ^c
• helical density map visualization analysis ^c

A component of the system's energy representing the potential energy stored in the bending of bond angles away from their equilibrium values. This term is usually modeled with a harmonic potential, governing the local geometry and stiffness of the molecular structure. High angle energy values can indicate regions of significant local strain in a molecule. Simulation outputs list this value as Angle, E_angle, or ANGLE. (UNVERIFIED)

The cc-pV6Z (correlation-consistent polarized Valence Sextuple-Zeta) basis set is even larger than cc-pV5Z, providing six functions per valence orbital and polarization functions up to i-type. It allows for further incremental improvement towards the complete basis set limit in highly accurate benchmark studies. It is computationally feasible only for very small atomic or diatomic systems. (UNVERIFIED)

match_atomname is a utility program within the AmberTools suite used as a quality control step in simulation setup. It functions by comparing two molecular structure files to ensure that their atom names and connectivity are identical. This check is crucial for preventing errors when processing large sets of conformations where atom ordering might have been inadvertently changed. (UNVERIFIED)

A volumetric analysis parameter that specifies the spacing between points in a 3D grid used for spatial analysis of simulation data. A smaller grid spacing yields a higher resolution grid but increases the computational cost of the grid-based calculation. This is a key parameter for controlling the resolution of the volumetric data. This is often set with the keyword spacing or grdspc. (UNVERIFIED)

A general state referring to a molecule (either ligand or receptor, or the complex) being surrounded by solvent molecules (typically water in biological contexts). This term emphasizes the presence and influence of the solvent on the molecule's structure, dynamics, and energetics. Both the bound and unbound states are typically solvated states, and solvation effects are crucial components of binding free energies and conformational preferences. (UNVERIFIED)

Lennard-Jones Particle Mesh Ewald (LJ-PME) is a computational algorithm that accurately calculates the long-range part of the van der Waals interactions in a periodic simulation. It applies the same efficient grid-based Ewald methodology used for electrostatics to the attractive (1/r^6) component of the Lennard-Jones potential, which is often neglected or truncated in standard simulations. Using LJ-PME is important for obtaining highly accurate pressure and surface tension values in simulations of homogeneous liquids or lipid membranes where long-range dispersion forces are significant. (UNVERIFIED)

A binary file format used by the GROMACS simulation package to store time-series data of system energies and thermodynamic properties. It records values such as potential energy components, temperature, pressure, and box dimensions at specified intervals in a portable, machine-independent format. For experts, this file (extension .edr) is accessed via the gmx energy tool to extract statistics or plotting data, and its binary nature ensures no loss of precision compared to text logs. (UNVERIFIED)

A system setup tool is a program designed to assemble all the components of a molecular simulation into a complete, simulation-ready model. This typically involves placing the main molecule in a simulation box, adding the correct number of solvent molecules, and introducing ions to neutralize the system's charge. For simulation experts, these tools automate the complex and error-prone process of building a periodic system that accurately represents the desired experimental conditions. (UNVERIFIED)

• membrane packing tool ^c
• topology and coordinate generation tool ^c
• thermodynamic integration similarity calculation tool ^c
• crystallographic build tool ^c
• system packing and solvation tool ^c

Time-lagged Independent Component Analysis (tICA) is an advanced analysis method used to identify the slowest, most persistent motions from a molecular dynamics simulation. It is a dimensionality reduction technique that finds the collective coordinates that change most slowly over a specific time lag, which are often the most important for understanding the system's long-timescale functional dynamics. These slow coordinates are frequently used as the basis for building Markov State Models to describe the system's kinetics. (UNVERIFIED)

An output file is generated by a computational program and contains the results of the calculation or simulation, along with logs, progress information, and any error messages. Its content varies greatly depending on the program and the type of task performed, but typically includes computed energies, optimized geometries, properties, and diagnostic information. These files are crucial for analyzing the outcome of computational jobs. (UNVERIFIED)

• analysis data ^c
• simulation log ^c
• simulation trajectory ^c
• simulation state ^c

The aug-cc-pV(D+d)Z basis set combines three features: a double-zeta correlation-consistent framework, augmentation with diffuse functions ('aug-'), and the additional d-function ('+d') primarily for second-row elements (Na-Ar). It is designed for calculations on second-row atoms where accurately describing anions, weak interactions, or response properties (requiring 'aug') is important, along with the improved polarization from '+d'. (UNVERIFIED)

• AMBER lib format

• An Amber OFF Library file (Object File Format) is a text file that stores a library of molecular units or residues, including their force field parameters, atom types, connectivity, and charges. These files are a fundamental part of the Amber software suite, allowing the LEaP program to build simulation-ready topology files for systems containing non-standard molecules or modified residues (like amino acids with post-translational modifications). The file extension can be interchangeably provided as .lib/.off files UNVERIFIED)

Membrane placement analysis is a computational method used to determine the optimal position and orientation of a protein structure within a lipid bilayer. It calculates the most energetically favorable alignment by assessing the hydrophobicity of the protein surface and matching it to the hydrophobic core and polar interfaces of the membrane. This analysis is a critical prerequisite for setting up stable membrane protein simulations and for understanding how proteins anchor themselves in the cell membrane. (UNVERIFIED)

A constraint algorithm similar to SHAKE but designed for velocity-Verlet type integrators, ensuring that both positions and velocities satisfy the constraint conditions at the end of each time step. It involves solving constraint equations for positions first, then using those positions to solve for constrained velocities. This maintains consistency between positions and velocities under constraint (UNVERIFIED).

A non-native contact map is a contact map that shows the atomic touches in a misfolded or unfolded protein structure that are not present in its correct, functional shape. It is used to identify incorrect or transient interactions that may form during a simulation, especially in the study of protein folding pathways or misfolded states. Analyzing non-native contacts is crucial for understanding the formation of misfolded intermediates and kinetic traps on the folding landscape. (UNVERIFIED)

The aug-cc-pV5Z basis set combines the quintuple-zeta correlation-consistent basis (cc-pV5Z) with an added set of diffuse functions. It is an extremely large basis set used for benchmark calculations aiming for near complete basis set limit accuracy for systems demanding accurate treatment of both correlation energy and diffuse electron density. Its use is limited to very small systems due to computational cost. (UNVERIFIED)

A numerical method used to solve the equations of motion in a simulation by updating positions and velocities at offset time intervals. It calculates velocities at half-integer time steps and positions at integer time steps, ensuring that the integration is time-reversible and symplectic (energy-conserving). For experts, while computationally efficient and stable (O(Δt ^2)), it does not provide velocities and positions at the same instant, requiring interpolation for calculating kinetic energy or pressure at step t. (UNVERIFIED)

Network analysis is a method that represents a molecule as a graph of nodes (atoms or residues) connected by edges (interactions or correlations) to analyze how information is communicated through its structure. By applying graph theory, this approach can identify critical residues that act as communication hubs and map the pathways of correlated motion that connect distant parts of the molecule. This is a powerful tool for understanding allosteric regulation and the long-range effects of mutations. (UNVERIFIED)

This is a 3D map that shows the average electrostatic energy of the solvent at different points in space, as calculated by the Particle Mesh Ewald (PME) method. The value at each grid point represents the electrostatic potential energy density of the solvent, revealing how the solvent's energy is distributed, particularly around a solute or at an interface. This analysis provides a detailed picture of the electrostatic environment created by the solvent and how it is perturbed by the presence of other molecules. (UNVERIFIED)

A molecular structure is the information that specifies the three-dimensional arrangement of atoms in a molecule. It is typically represented by a list of atomic coordinates (X, Y, Z) for each atom in the system. This structural information is the fundamental input for visualization and is the starting point for any molecular simulation. (UNVERIFIED)

A type of constraint and restraint parameter that specifies how geometric constraints are applied to the system, typically to fix the length of bonds involving hydrogen. This allows for a longer simulation time step. The constraint parameter settings are crucial for the efficiency of many biomolecular simulations. These are often set with keywords like ntc or constraints. (UNVERIFIED)

• constrained bonds ^c
• SHAKE tolerance ^c
• constraint algorithm parameter ^c

A specific computational task within a free energy calculation framework that uses the Fragment Molecular Orbital (FMO) method to determine the energy and properties of a molecule in its unbound ('free') state. This is often required when calculating binding free energies, where the energy of the isolated components serves as a reference point (G free). Employing FMO makes such quantum mechanical calculations feasible for the large molecules often involved in biomolecular binding events. (UNVERIFIED)

A component of the system's energy representing the potential energy associated with the rotation around a covalent bond, defined by a sequence of four bonded atoms. This term, also known as torsional energy, governs the conformational preferences and rotational barriers within a molecule. The dihedral energy is critical for correctly sampling the different conformations a molecule can adopt. Simulation log files report this value as Dihedral, E_dihed, or DIHED. (UNVERIFIED)

A structure modification method is a computational procedure that alters the atomic coordinates or composition of a molecular structure file. This includes a wide range of operations such as adding or deleting atoms, rotating or translating molecules, or building new polymeric chains. For researchers, these methods are the fundamental tools used to build, edit, and prepare molecular models for simulation. (UNVERIFIED)

A specific type of atomic charge that is calculated by fitting point charges to reproduce the electrostatic potential surrounding the molecule, as determined by a quantum mechanical calculation. These ESP charges are designed to provide a realistic representation of the molecule's external electric field. They are often used for parameterizing new molecules for simulation. This is a standard output of programs like RESP or antechamber. (UNVERIFIED)

A type of miscellaneous descriptor representing the matrix of the second derivatives of the potential energy with respect to the atomic coordinates. The hessian describes the curvature of the potential energy surface. It is used to calculate vibrational frequencies and to characterize stationary points on the energy landscape. This is a key output of frequency calculations. (UNVERIFIED)

Software specifically designed for creating interactive 3D graphical representations of molecular structures, densities, surfaces, and dynamic trajectories generated from simulations or experiments. These tools allow researchers to visually inspect molecular details, understand complex spatial relationships, analyze interactions, monitor simulations, and create figures and animations for communication. Common examples include VMD, PyMOL, Chimera/ChimeraX, and DeepView (Swiss-PdbViewer). (UNVERIFIED)

• data plotting tool ^c
• molecular structure visualization tool ^c

Multi-Reference Configuration Interaction with Single and Double excitations, a quantum chemistry method that accounts for electron correlation by performing a configuration interaction calculation (including configurations generated by single and double electron excitations) starting from a multi-reference wavefunction (e.g., from CASSCF). Like MR-CCSD, it targets high accuracy for electronically complex systems but is computationally demanding and may suffer from size-consistency issues depending on the formulation. It offers an alternative way to add dynamic correlation to a multi-reference description (UNVERIFIED).

The cc-pVQZ (correlation-consistent polarized Valence Quadruple-Zeta) basis set further increases accuracy by providing four functions for each valence orbital and higher angular momentum polarization functions (up to g-type for second-row atoms). It aims to capture a larger percentage of the electron correlation energy than cc-pVTZ, approaching the complete basis set limit more closely. It is computationally demanding and used for high-accuracy calculations. (UNVERIFIED)

The aug-cc-pV5Z-RI basis set is the corresponding auxiliary basis developed for Resolution of Identity (RI) or Density Fitting (DF) methods used in conjunction with the very large aug-cc-pV5Z orbital basis. It facilitates the use of RI/DF integral approximations, which is often crucial for making calculations with the demanding aug-cc-pV5Z basis computationally feasible. (UNVERIFIED)

Third-order SCC-DFTB, or DFTB3, is a further refinement of the SCC-DFTB semi-empirical method. It includes a third-order correction term in the expansion of the DFT total energy, which improves the description of hydrogen bonding and proton affinities. For experts, DFTB3 is a more accurate and robust method than earlier versions, particularly for systems where hydrogen bonds play a critical role. (UNVERIFIED)

The hybrid solvent MM/PBSA method is a technique for estimating binding free energy that combines a detailed, explicit solvent model for the region close to the molecule with a faster, continuum model for the bulk solvent. This approach aims to capture the specific, crucial interactions of nearby water molecules while maintaining the computational efficiency of an implicit solvent model for the overall calculation. The final free energy is calculated using the standard MM/PBSA framework but is derived from a simulation that uses this more complex, multi-layered solvent representation. (UNVERIFIED)

A specific electronic structure analysis technique used to partition the total electron density of a molecule and assign partial atomic charges to individual atoms. Various schemes exist (e.g., Mulliken, Löwdin, Hirshfeld, Natural Population Analysis, ESP-derived charges), each with different theoretical underpinnings, providing insights into charge distribution, polarity, and electrostatic interaction sites. These charges are often used to parameterize classical force fields or interpret reactivity. (UNVERIFIED)

• Mulliken charge analysis ^c
• CHELPG charge analysis ^c

An extension of the Andersen barostat that allows the simulation box shape and volume to change anisotropically, meaning the lengths of the box edges and the angles between them can fluctuate independently. This is crucial for simulating phase transitions or studying materials under anisotropic stress conditions while correctly sampling the NPT ensemble. It uses a matrix of barostat variables coupled to the pressure tensor (UNVERIFIED).

The DCD (.dcd) trajectory format is a widely used binary file format for storing atomic coordinates from molecular dynamics simulations, optionally including periodic box information. Originally developed for CHARMM, it is now supported by many simulation packages (like NAMD, LAMMPS) and analysis tools (like VMD) due to its efficiency and portability. It typically stores coordinates in single precision. (UNVERIFIED)

The state in which a ligand molecule is not associated with the receptor molecule, typically solvated freely in the surrounding solvent (e.g., water) or located far from the receptor's binding site. Defining the unbound state is necessary for calculating binding free energies, as it serves as the reference state relative to the bound state. It represents the ligand and receptor separated and independently solvated. (UNVERIFIED)

In statistical mechanics and molecular simulation, an ensemble is a theoretical construct representing an infinite collection of identical systems, each in a different possible microscopic state (defined by positions and momenta of all particles) but all corresponding to the same macroscopic thermodynamic state defined by a set of fixed variables (e.g., N, V, T or N, P, T). Molecular simulations generate trajectories that sample the microscopic states belonging to a specific ensemble, allowing the calculation of macroscopic properties as averages over these states. The choice of ensemble (e.g., NVE, NVT, NPT) determines which macroscopic variables are held constant during the simulation, mimicking specific experimental conditions. (UNVERIFIED)

• microcanonical ensemble ^c
• grand canonical ensemble ^c
• isothermal-isobaric ensemble ^c
• canonical ensemble ^c

A fundamental distribution analysis method that calculates the probability of finding a particle (e.g., a solvent atom like oxygen) at a given distance 'r' from a central reference point (e.g., a solute atom or the solute's center of mass), relative to the probability expected for a uniform distribution at that distance. The resulting function, the radial distribution function or RDF, often denoted g(r), typically shows peaks corresponding to ordered solvation shells and decays to 1 at large distances (bulk solvent). Integration of the first peak gives the average coordination number in the first solvation shell. (UNVERIFIED)

A multiscale simulation method is a technique that combines two or more different levels of theoretical description to model a single system. This is often done to study a large system where a small, critical part requires a high-accuracy quantum mechanical treatment while the larger environment can be modeled with a faster, classical force field. For experts, methods like QM/MM are powerful multiscale approaches for studying chemical reactions in enzymes. (UNVERIFIED)

A measure of the useful energy available to do work in a system held at constant temperature and volume. It is a thermodynamic potential defined as the internal energy minus the product of temperature and entropy (A=U−TS). For experts, this quantity is the natural free energy ensemble for NVT (canonical) simulations and is often calculated using methods like thermodynamic integration or Bennett acceptance ratio. (UNVERIFIED)

This term categorizes different strategies for generating and utilizing molecular dynamics trajectories when calculating binding free energies using endpoint methods like MM/PBSA or MM/GBSA. These approaches primarily differ in whether separate simulations are run for the complex, free protein, and free ligand, or if data for all components are derived from a single simulation. The choice affects computational cost and potentially accuracy due to sampling differences. (UNVERIFIED)

• single trajectory ^c
• 3 trajectory approach ^c
• 1 trajectory approach ^c

A closure relation is a necessary mathematical approximation used in the Reference Interaction Site Model (RISM) theory to solve its complex equations. It provides a way to relate two different unknown correlation functions, effectively "closing" the system of equations so that a unique solution can be found. The choice of a specific closure relation is a key part of the RISM model that determines its accuracy for different types of molecular liquids. (UNVERIFIED)

Ligand pairs selection criteria refer to the set of guiding principles and factors considered when choosing pairs of ligands for comparative computational studies, particularly for relative binding free energy calculations. The goal is to select pairs that are sufficiently similar to ensure reliable calculations but also diverse enough to provide meaningful insights. These criteria help optimize the design and feasibility of computational drug discovery campaigns. (UNVERIFIED)

• structural changes ^c
• ligand efficiency ^c
• computational feasibility ^c
• relevance to drug discovery ^c
• structural data quality ^c
• experimental data availability ^c
• binding affinity range ^c
• chemical properties ^c
• structural similarity ^c
• structural and chemical diversity ^c
• chemical similarity ^c
• stability in simulations ^c

A comprehensive molecular similarity measure that combines both shape-based RefTversky and chemical feature-based RefColorTversky scores into a single metric. This combined measure provides a more complete assessment of molecular similarity by considering both geometric shape and chemical functionality simultaneously. The resulting score typically ranges from 0 to 2, though it can occasionally exceed this range due to the field-based nature of shape matching.

A residue connection atom is the specific atom within a residue that is designated to form a chemical bond with an adjacent residue in a polymer. For example, in a protein, the nitrogen atom of one amino acid is the connection atom that bonds to the carbonyl carbon of the previous one. For system building tools, identifying these connection atoms is essential for correctly assembling a polymer chain from its constituent residue units. (UNVERIFIED)

An algorithm for finding the shortest path between a starting node and all other nodes in a graph with non-negative edge weights. It works by iteratively exploring the graph, maintaining the shortest distance found so far to each node, and always extending the path from the node with the current shortest distance. It is fundamental in graph theory and network routing (UNVERIFIED).

An efficient algorithm for calculating long-range forces (like electrostatic or gravitational) in particle simulations, conceptually similar to Particle Mesh Ewald (PME). It splits the force calculation into a short-range part computed directly between nearby particles (particle-particle) and a long-range part computed using a grid and Fast Fourier Transforms (particle-mesh). PPPM is widely used in both astrophysics and molecular simulation for its performance and accuracy (UNVERIFIED).

A Markov State Model (MSM) is a statistical model constructed from molecular simulation data to describe the long-timescale dynamics of the system. It involves partitioning the vast conformational space into a set of discrete states and estimating the probabilities of transitioning between these states based on observed simulation trajectories. MSMs can predict long-time kinetic properties, like folding times or equilibrium populations, even from ensembles of relatively short simulations. (UNVERIFIED)

TCPB-cpp is a software tool that acts as a bridge, allowing a classical simulation program to communicate with the TeraChem quantum chemistry program. It is a C++ library that provides an Application Programming Interface (API), enabling a molecular dynamics engine to send a small, quantum mechanical (QM) part of the system to TeraChem for a high-performance, GPU-accelerated energy and force calculation. This allows for the creation of powerful and efficient QM/MM simulations, where the speed of a classical simulation is combined with the accuracy of TeraChem's quantum calculations for studying chemical reactions. (UNVERIFIED)

A general term for a similarity score obtained by combining results from multiple different similarity calculation methods or metrics. The rationale is often to capture different aspects of similarity (e.g., structural, feature-based) into a single, potentially more informative score. The specific combination formula and constituent metrics define the particular combo score (UNVERIFIED).

Trajectory meta-analysis refers to a higher level of analysis that involves comparing, contrasting, or combining the results from multiple, independent simulation trajectories. This can be used to improve statistical certainty, assess the convergence of a simulation, or identify the differences in dynamics between a wild-type protein and a mutant. For experts, this approach is essential for drawing robust conclusions that are not dependent on a single simulation run. (UNVERIFIED)

An umbrella sampling analysis parameter that specifies the increment or step size used when assessing the convergence of the calculated Potential of Mean Force (PMF). The PMF is calculated using progressively larger amounts of data to check for convergence. The potential of mean force convergence step size is a key parameter for ensuring that the calculated free energy profile is reliable. This is a key parameter for WHAM analysis. (UNVERIFIED)

The CCP4 map format is an industry-standard file format used in structural biology, particularly in X-ray crystallography and cryo-electron microscopy (Cryo-EM). It is designed to store three-dimensional volumetric data, most commonly representing electron density. These maps allow scientists to visualize the shape of molecules like proteins and nucleic acids. (UNVERIFIED)

Clustering analysis encompasses algorithms designed to partition a dataset into distinct groups or clusters, such that data points within the same cluster are more similar to each other than to those in other clusters based on chosen features. In molecular simulation, clustering is frequently applied to trajectory data to identify distinct conformational states visited by the system. Various algorithms exist, differing in how similarity and clusters are defined (e.g., k-means, hierarchical clustering). (UNVERIFIED)

An RMSD calculation algorithm is the computational procedure used to quantify the difference between two molecular structures by calculating their Root-Mean-Square Deviation. The algorithm first optimally superimposes the two structures in 3D space to minimize the distances between corresponding atoms. It then calculates the root-mean-square average of these distances, providing a single numerical measure of structural similarity. (UNVERIFIED)

• Kabsch RMSD algorithm ^c
• quaternion RMSD algorithm ^c

An accelerated MD parameter that specifies the energy threshold for the dihedral energy, below which the boost potential is applied. This parameter controls when the dihedral energy term is biased. The aMD dihedral energy threshold is a key parameter for tuning the aMD simulation. This is often set with the keyword EthreshD. (UNVERIFIED)

Analysis data is the information content that is the result of processing raw simulation output. This includes any derived quantities calculated from a trajectory, such as RMSD values over time, a potential of mean force profile, or a list of identified hydrogen bonds. This processed data represents the scientific findings extracted from the simulation. (UNVERIFIED)

A specific variant of the TIP4P water model, parameterized specifically to reproduce the properties of different phases of ice (solid water), as well as liquid water properties. It aims to provide a better description of water's phase diagram, particularly the solid phases, compared to models optimized solely for the liquid state. It is useful for studying freezing, melting, or ice interfaces. (UNVERIFIED)

A software suite is a collection of distinct computer programs that are packaged and distributed together to provide a comprehensive set of functionalities. These suites typically share a common installation process and often use compatible file formats to allow data to flow between the different tools in the package. (UNVERIFIED)

• AmberTools ^c
• TINKER ^c
• Spartan ^c
• YASARA ^c
• SYBYL ^c
• X-PLOR ^c
• Abalone ^c
• SAMSON ^c
• HyperChem ^c
• TURBOMOLE ^c
• CHARMM ^c
• GROMOS ^c
• GROMACS ^c
• MoFT ^c
• AMBER ^c

A freely available software package for molecular mechanics and dynamics simulations. TINKER provides implementations of various standard force fields (AMBER, CHARMM, OPLS, MMFF) and includes tools for energy minimization, MD simulation, free energy calculations, and structural analysis. It is particularly notable for its implementation of polarizable force fields (e.g., AMOEBA) and its modular design. (UNVERIFIED)

FFTW is a highly optimized software library for computing the discrete Fourier transform, a fundamental mathematical operation used in many scientific applications. In biomolecular simulations, it is most commonly used to perform the Fast Fourier Transform (FFT) required for the Particle Mesh Ewald (PME) method of calculating long-range electrostatic forces. For simulation engines, using the FFTW library is essential for achieving high performance in the most computationally demanding part of the simulation. (UNVERIFIED)

The RISM model is a sophisticated theoretical method used to predict how solvent molecules, like water, will arrange themselves around a central molecule. The Reference Interaction Site Model (RISM) is a statistical-mechanical theory of molecular liquids that calculates the distribution of solvent atoms around a solute by solving a set of integral equations. It provides a detailed, atomistic picture of the solvation structure and can be used to calculate thermodynamic properties like the solvation free energy, offering a powerful alternative to explicit solvent simulations. (UNVERIFIED)

• closure relation ^c
• 1D-RISM model ^c
• dielectrically consistent RISM model ^c
• 3D-RISM model ^c

The Amber evecs eigenvector file is a specialized output from Principal Component Analysis (PCA), normal mode analysis, or quasiharmonic analysis in AMBER (using cpptraj or ptraj). This file stores the eigenvectors (or “principal modes”) and eigenvalues resulting from the diagonalization of a covariance or mass-weighted covariance matrix, commonly used in essential dynamics analysis of molecular simulations. The output file is usually called evecs.dat, evecs.out, or follows a similar naming scheme. There is no fixed "file extension" required; however, the content and formatting are standardized for compatibility with AMBER utilities (e.g., cpptraj, ptraj),

The single trajectory approach, often used in MM/PBSA and MM/GBSA calculations, involves running only one molecular dynamics simulation of the protein-ligand complex. Snapshots of the complex, the protein alone, and the ligand alone are then extracted directly from this single trajectory for endpoint free energy calculations. This reduces the computational cost compared to running three separate simulations but assumes the conformations sampled in the complex are representative for the free states. (UNVERIFIED)

An electrostatic parameter that specifies the algorithm used to calculate long-range electrostatic interactions in a periodic system. Common choices include Particle Mesh Ewald (PME), Ewald sum, or reaction field methods. The choice of long-range electrostatic method parameter is one of the most important for the accuracy of simulations of biomolecules. This is often set with keywords like ewald or coulombtype. (UNVERIFIED)

A random acceleration MD parameter that specifies the strength of the acceleration boost applied in a Random Acceleration Molecular Dynamics (RAMD) simulation. This parameter controls the magnitude of the random forces used to accelerate the system's exploration. The RAMD boost strength is a key parameter for tuning the RAMD simulation. This is often set with the keyword ramdboost. (UNVERIFIED)

A process specification is the abstract set of instructions and parameters that define how a computational task, like a simulation or an analysis, should be performed. It represents the complete plan for the process, including the choice of algorithms, control settings, and input files. This specification is what must be recorded to ensure a computational experiment is fully reproducible. (UNVERIFIED)

• analysis script ^c
• simulation parameter set ^c

Hydrogen bond analysis is a structural analysis method used to identify and quantify the hydrogen bonds that are formed and broken during a simulation. The analysis typically uses a set of geometric criteria, such as a maximum distance between the donor and acceptor atoms and a minimum angle, to define when a hydrogen bond exists. For researchers, tracking the number and lifetime of hydrogen bonds is a fundamental way to understand the stability of protein and nucleic acid structures. (UNVERIFIED)

A category of data formats used by the CHARMM simulation package to describe the molecular topology of a system. These formats define the atoms, connectivity, and the chemical nature of residues. (UNVERIFIED)

PDDG/PM3 is a specific semi-empirical quantum mechanical method that is a modification of the standard PM3 method. The PDDG (Pairwise Distance Directed Gaussian) part refers to the addition of Gaussian correction functions to the core-core repulsion terms to improve the description of non-covalent interactions. For experts, PDDG/PM3 is a refinement that aims to provide better accuracy for intermolecular interaction energies compared to the original PM3 method. (UNVERIFIED)

A text-based file format used by GROMACS to define specific subsets or groups of atoms within a molecular system. It lists atom indices assigned to named groups, allowing users to apply specific actions (like thermostatting, restraining, or analyzing) to just those selected parts. For experts, this file (extension .ndx) is generated by gmx make_ndx and is essential for setting up non-standard simulation protocols where default groups like "Protein" or "Solvent" are insufficient. (UNVERIFIED)

A surface area calculation algorithm is a procedure used to compute the area of a molecule's surface that is accessible to a solvent. This is a key analysis for understanding how a molecule interacts with its environment. For experts, this category includes specific algorithms like the Shrake-Rupley method or the LCPO algorithm, which are essential for implicit solvent models and for characterizing protein packing and cavities. (UNVERIFIED)

• LCPO algorithm ^c
• Shrake-Rupley algorithm ^c
• ICOSA algorithm ^c

This is a specialized force field for simulating proteins that pays extra attention to how proteins interact with water and charged ions. The AMBER ff15ipq force field was developed to improve the description of protein interactions with ions by using a novel charge model (Implicitly Polarized Charge, IPq) that better reproduces experimental hydration free energies. This force field is particularly recommended for simulations where the accurate modeling of protein-ion interactions or salt bridge dynamics is critical to the system's behavior. (UNVERIFIED)

Lebedev quadrature is a specific numerical integration algorithm designed for accurately integrating functions over the surface of a sphere. It uses a predefined set of points and weights on the sphere that are optimized for high efficiency. For computational chemists, this algorithm is a standard and critical component of Density Functional Theory (DFT) calculations for evaluating the angular part of the exchange-correlation functional. (UNVERIFIED)

Information or data obtained directly from an individual researcher or expert through informal means such as email, conversation, or unpublished notes, rather than through a formal publication or public database. While sometimes necessary, such sources are typically less verifiable and are often used for supplementary or preliminary information. (UNVERIFIED)

A unit which is a standard measure of the amount of a 2-dimensional flat surface.

OPM database (Orientations of Proteins in Membranes) is both a database and a web server/tool providing pre-calculated transmembrane orientations and positions for experimentally determined membrane protein structures found in the PDB. OPM uses a computational approach based on minimizing the calculated transfer free energy from water to the lipid bilayer to determine the most likely membrane boundaries and protein position relative to the bilayer center. It's a valuable resource for obtaining initial membrane protein placements for simulations. (UNVERIFIED)

• membrane protein orientation tool ^c
• database web server ^c

A specific type of thermal properties analysis focused on quantifying the heat absorbed or released during chemical reactions or phase transitions, often involving the calculation of enthalpies of formation, reaction enthalpies, or activation enthalpies. Typically employing quantum mechanical methods or specialized simulation setups, this analysis provides fundamental data on the energetics of chemical transformations. It helps predict reaction feasibility and energy output/input. (UNVERIFIED)

The BAR/PBSA method is a hybrid free energy calculation technique that combines the Bennett Acceptance Ratio (BAR) method with MM/PBSA endpoint calculations. It likely uses BAR to calculate the free energy change for a short-range, explicit part of the system, and then adds a correction for the long-range solvation effects using the faster MM/PBSA method. For experts, this represents a multi-step approach to balance the rigor of alchemical methods with the efficiency of continuum solvent models. (UNVERIFIED)

A type of quantum mechanics basis set consisting of periodic sine and cosine functions (waves) defined by their direction and wavelength. Plane waves are particularly well-suited for calculations on periodic systems like crystals or surfaces, often used in conjunction with Density Functional Theory and pseudopotentials. Their systematic improvability by increasing the number of waves (controlled by an energy cutoff) is a key advantage in solid-state simulations (UNVERIFIED).

A central focus within thermodynamics analysis aiming to compute the free energy (typically Gibbs or Helmholtz free energy) of a system or, more commonly, the free energy difference (ΔG or ΔA) between different states (e.g., bound vs. unbound, folded vs. unfolded). Free energy combines energy (enthalpy) and disorder (entropy) to determine the thermodynamic favorability and equilibrium position of molecular processes under constant temperature and pressure/volume. Calculating free energies often requires enhanced sampling MD techniques or other specialized computational methods complementary to basic MD. (UNVERIFIED)

• 3D reference interaction site analysis ^c
• free state FMO analysis ^c
• BAR/PBSA analysis ^c
• lambda-dynamics free energy analysis ^c
• binding free energy calculation analysis ^c
• Gaussian fluctuation free energy analysis ^c
• lambda-scheduling free energy analysis ^c
• weighted thermodynamic perturbation theory analysis ^c
• PC+ correction analysis ^c
• potential mean force analysis ^c
• universal correction analysis ^c
• variational free energy profile analysis ^c
• EMIL free energy analysis ^c

A stochastic simulation method that relies on repeated random sampling to explore the configurational space of a molecular system. Unlike molecular dynamics, which integrates equations of motion over time, Monte Carlo generates a sequence of states by proposing random trial moves (such as atom displacements or molecular rotations) and accepting or rejecting them based on a thermodynamic probability criterion, typically the Metropolis algorithm. It is widely used for calculating equilibrium thermodynamic properties and sampling conformational ensembles. (UNVERIFIED)

Constant pH replica-exchange molecular dynamics is an advanced enhanced sampling method that combines constant pH simulations with the replica-exchange technique. It runs multiple simulations in parallel, each at a different target pH value, and periodically attempts to swap coordinates between them. For experts, this method dramatically enhances the sampling of both conformational and protonation state space, making it a powerful tool for studying complex pH-dependent phenomena. (UNVERIFIED)

Thermodynamic Integration (TI) is a rigorous statistical mechanics method used to calculate free energy differences between two defined states (e.g., A and B) by simulating a reversible, non-physical transformation pathway connecting them. It involves calculating the ensemble average of the derivative of the system's energy with respect to a coupling parameter (λ) at several points along the path and integrating this derivative over the path (ΔG=∫01 ⟨∂H/∂λ⟩ λdλ). This framework encompasses various specific approaches and implementation details. (UNVERIFIED)

• thermodynamic integration approach ^c
• thermodynamic integration extrapolation approach ^c

Molecular topology is the information that describes the chemical connectivity and properties of a molecule for a simulation. It includes the list of atoms, the bonds connecting them, and the assignment of atom types and partial charges from a specific force field. The topology provides the blueprint that the simulation engine uses to know how to calculate the forces between atoms. (UNVERIFIED)

• force field parameterization descriptors ^dp
• topological counts ^dp
• constraint descriptors ^dp

A computational tool designed to predict or determine the likely orientation and transmembrane embedding depth of a protein structure within a lipid bilayer. Correctly positioning a membrane protein in the bilayer is a critical first step for setting up realistic membrane protein simulations. These tools often use algorithms based on hydrophobicity analysis, sequence features, or structural properties to find the most favorable position relative to the hydrophobic core and hydrophilic headgroup regions of the membrane. Examples include OPM, PPM, MemProtMD, and MemEmbed. (UNVERIFIED)

• orientations of proteins in membranes ^c
• memembed ^c

A .binpos file is a binary format used to store atomic coordinate frames from a molecular dynamics simulation. The name itself stands for "binary position." This format is often referred to as the "Scripps 'binpos' format" and is recognized by Amber's analysis tools like cpptraj and other programs such as VMD.

A system setup parameter that specifies the chemical state of the N- and C-termini of a polymer chain. This parameter indicates whether the termini are neutral (capped) or charged (uncapped). The molecular termini state is a key descriptor of the chemical composition of the simulated protein or nucleic acid. This is often controlled by a termini capping flag. (UNVERIFIED)

A specific type of solvent analysis focusing on the direct interaction of water molecules with a solute molecule. It involves characterizing the arrangement, orientation, dynamics, and energetics of water molecules in the immediate vicinity of the solute, often referred to as the hydration shell(s). Understanding hydration patterns is critical as these interfacial water molecules strongly influence the solute's structure, stability, dynamics, and interactions with other molecules. (UNVERIFIED)

An analysis script contains a sequence of commands or code written for a specific analysis program or library (like Amber's cpptraj, VMD's Tcl interface, or Python libraries like MDAnalysis). These scripts automate the process of reading simulation output data (especially trajectories) and performing calculations such as RMSD, hydrogen bond analysis, distance measurements, or principal component analysis. They define the workflow for extracting meaningful insights from raw simulation data. (UNVERIFIED)

A force field that explicitly includes parameters for every atom in the simulated system, including hydrogen atoms. This approach provides a high level of detail and aims for greater physical realism compared to coarse-grained models. All-atom simulations are generally more computationally intensive due to the larger number of particles. (UNVERIFIED)

The GROMACS XPM file is an ASCII text file format used by the GROMACS molecular dynamics suite to store two-dimensional matrix data. It is a specialized application of the general XPixMap (.xpm) format, adapted to represent scientific data such as distance matrices, root-mean-square deviation (RMSD) matrices, or hydrogen bond patterns. The format is human-readable and designed for easy visualization. It encodes numerical data as a color-coded image defined by characters, making it viewable with standard XPM viewers and convertible into graphical formats like PostScript using GROMACS utilities such as gmx xpm2ps. (UNVERIFIED)

A membrane protein system is a specific type of protein system where the protein is embedded within a lipid bilayer, mimicking its native environment in a cell membrane. These are among the most complex and computationally demanding types of simulations to set up and run. For experts, these simulations are essential for understanding the function of a huge class of proteins that act as channels, transporters, and receptors in the cell. (UNVERIFIED)

A time-averaged restraint simulation is an advanced simulation method where the restraining potential is applied not to the instantaneous structure, but to the average of a property over a period of time. This is particularly useful for incorporating experimental data, like from NMR, which is also an average over time and a molecular ensemble. For experts, this method provides a more physically meaningful way to enforce experimental restraints that reflect the dynamic nature of the molecule. (UNVERIFIED)

Periodic boundary imaging is a fundamental post-processing step in structural analysis that is used to make simulation trajectories easier to visualize. It corrects for the fact that molecules can become "broken" or jump across the box when they cross a periodic boundary. The imaging algorithm translates the coordinates of the atoms to ensure that molecules remain whole and centered in the box, providing a continuous and visually coherent movie of the dynamics. (UNVERIFIED)

A Gaussian accelerated MD parameter that specifies the upper limit of the standard deviation for the potential energy boost. This parameter controls the maximum strength of the applied bias. The GaMD potential boost stddev limit is a key parameter for tuning the GaMD simulation. This is often set with keywords like sigma0P or sigma0D. (UNVERIFIED)

A specialized local structure analysis used to describe and quantify the non-planar conformation (puckering) of cyclic molecular fragments, particularly five-membered (e.g., furanose rings in DNA/RNA, proline) or six-membered rings (e.g., pyranose rings, cyclohexane). It employs parameters like pseudorotation angles and amplitudes to precisely define the ring's shape (e.g., envelope, twist, chair, boat conformations). This analysis is vital for understanding the structure and function of nucleic acids and carbohydrates. (UNVERIFIED)

• Altona & Sundaralingam pucker analysis ^c
• Cremer & Pople pucker analysis ^c

A QM/MM parameter that specifies the total integer charge of the quantum mechanical (QM) region. This is a critical parameter for ensuring that the QM calculation is performed with the correct electronic state. The QM charge must be set correctly for the QM/MM simulation to be physically meaningful. This is often set with the keyword qmcharge. (UNVERIFIED)

Gibbs sampling replica exchange is an advanced simulation method used to efficiently explore the different shapes and energy states of a molecule. Unlike standard replica exchange which attempts to swap temperatures between neighboring simulations, this method attempts to swap configurations among all running simulations simultaneously based on a global probability criterion. For experts, this approach replaces the Metropolis swap criterion with a Gibbs sampling scheme, potentially increasing the rate of round-trips in temperature space and reducing the bottleneck of diffusion between adjacent replicas. (UNVERIFIED)

A component of entropy that arises from the translational motion of molecules. It quantifies the disorder associated with the possible positions of a molecule's center of mass. The translational entropy is a key component of the total entropy of a system. This value is often reported as dTStrans in quasi-harmonic analysis outputs. (UNVERIFIED)

Ab initio methods (Latin for "from the beginning") are a class of quantum chemistry computational techniques that solve the electronic Schrödinger equation based solely on fundamental physical constants and the identities of the atoms involved, without using parameters derived from experimental data. These methods, like Hartree-Fock and subsequent correlation methods (MPn, Coupled Cluster), aim for high accuracy based on first principles but are typically computationally expensive. They contrast with empirical or semi-empirical methods. (UNVERIFIED)

A computational tool or script that implements the MM/PBSA (Molecular Mechanics / Poisson-Boltzmann Surface Area) method for estimating free energy changes, typically ligand binding affinities or solvation free energies. This approach involves calculating molecular mechanics energies (MM), electrostatic solvation free energies using the Poisson-Boltzmann (PB) equation, and non-polar solvation free energies using a term proportional to the Solvent Accessible Surface Area (SASA), usually averaged over snapshots from an MD trajectory. It's an endpoint free energy method, computationally cheaper than FEP or TI but generally considered less rigorous. (UNVERIFIED)

• MMPBSA.py ^c
• molecular mechanics Poisson-Boltzmann surface area module ^c

Ensemble trajectory analysis is a method that involves analyzing a large collection of independent simulation trajectories together, rather than just a single long one. This approach provides a more robust and statistically reliable picture of a molecule's behavior by sampling a wider range of starting conditions and potential pathways. It is particularly important for studying complex processes like protein folding or for achieving converged statistics on a system's properties. (UNVERIFIED)

CHARMM commonly uses coordinate files in its own CARD format (.crd), which is a formatted ASCII file including atom coordinates along with atom numbers, residue names/numbers, atom types, and possibly weighting factors. It often starts with a title section describing the system. CHARMM also readily reads and writes coordinates in the standard Protein Data Bank (PDB) format. (UNVERIFIED)

A DNA-ligand system is a specific type of ligand complex system composed of a DNA molecule interacting with a small molecule ligand. These simulations are used to study how drugs or other small molecules bind to DNA, which can be a mechanism for anti-cancer or anti-viral therapies. For experts, these systems are important for understanding intercalation, groove binding, and the structural changes induced in DNA upon ligand binding. (UNVERIFIED)

A script is a computer program, usually written in a high-level scripting language like Python or Perl, that automates a sequence of tasks. Unlike a compiled simulation engine, a script is interpreted directly to execute a series of commands or operations. In biomolecular simulation, scripts are essential for automating repetitive tasks such as preparing input files, submitting jobs to a cluster, and processing output data. (UNVERIFIED)

• custom script ^c
• automation script ^c
• workflow script ^c
• utility script ^c
• data analysis script ^c

Minimization is a computational step that relaxes a molecular structure to remove any bad clashes between atoms. As a stage of the preparation process, energy minimization is a procedure that adjusts the atomic coordinates to find a nearby local minimum on the potential energy surface, thereby removing steric strain from the initial model. This is achieved by using algorithms like steepest descent or conjugate gradient to iteratively reduce the net forces on the atoms until a convergence criterion, such as grms_tol, is met. This process is referred to in log files and inputs with terms like "MINIMIZATION," "ntmin=1," "emtol," and "ncyc." (UNVERIFIED)

An ion concentration calculation method is the procedure used to determine the exact number of positive and negative ions that need to be added to a simulation box to achieve a target salt concentration. This calculation must account for the volume of the box and the number of counter-ions already added to neutralize the solute molecule. For experts, accurately performing this calculation is a mandatory step for preparing a system that correctly models the desired ionic strength. (UNVERIFIED)

A common method for calculating the distance between two points (e.g., representing molecules in a multi-dimensional property space or conformations by atom coordinates) based on the straight-line distance in that space. It is calculated as the square root of the sum of squared differences between corresponding coordinates or features. Lower Euclidean distance implies higher similarity in the context of the chosen space (UNVERIFIED).

A system setup parameter that specifies the pH value of the solution being simulated. The pH affects the protonation states of titratable residues in proteins and ligands. This is a critical parameter for ensuring that the simulation accurately represents the experimental conditions. This is often set with the keyword solvph. (UNVERIFIED)

A thermostat algorithm that maintains temperature by introducing stochastic collisions between randomly selected particles and fictitious heat bath particles. When a particle "collides," its velocity is reassigned from a Maxwell-Boltzmann distribution corresponding to the target temperature. This method correctly generates configurations from the canonical (NVT) ensemble (UNVERIFIED).

A method (often abbreviated GB/SA) for calculating the free energy of solvation, similar to PB/SA, but using a Generalized Born (GB) model instead of the Poisson-Boltzmann equation to compute the electrostatic contribution. It combines the GB electrostatic energy with a non-polar energy term proportional to the solvent-accessible surface area (SASA). GBSA offers a computationally much cheaper alternative to PB/SA for estimating solvation free energies, suitable for use during simulations or large-scale analyses, though potentially less accurate depending on the GB implementation and system. (UNVERIFIED)

YAML is a human-readable data serialization format that relies on indentation to define structure, making it exceptionally easy to read and edit. In the context of computational chemistry, it is frequently employed for configuration files, defining software environments (e.g., Conda), and specifying parameters for automated simulation workflows and pipelines. (UNVERIFIED)

Isotropic reorientational eigenmode dynamics is an advanced dynamics analysis method used to study the overall rotational motion of a molecule. It decomposes the complex tumbling of a molecule in solution into a set of simpler, independent rotational modes, or eigenmodes. For experts, this method provides a detailed picture of the molecule's rotational diffusion, which can be compared to experimental data from techniques like NMR relaxation. (UNVERIFIED)

A DIIS parameter that specifies the number of DIIS extrapolation attempts to be made to aid SCF convergence. This parameter controls how aggressively the DIIS algorithm is applied. The DIIS attempts is a key parameter for tuning the SCF convergence. This is often set with the keyword ndiis_attempts. (UNVERIFIED)

The cc-pVTZ (correlation-consistent polarized Valence Triple-Zeta) basis set provides three functions for each valence orbital, along with appropriate polarization functions (d,f for heavy atoms; p,d for H) optimized for correlation energy recovery. It offers substantially higher accuracy than cc-pVDZ for correlated calculations and is widely used as a good balance between accuracy and computational cost for many applications. (UNVERIFIED)

A specific type of polarizability that describes the non-linear response of a molecule's electron cloud to a strong external electric field. It is relevant for describing non-linear optical phenomena. The hyperpolarizability is an advanced electronic property calculated using high-level quantum chemistry methods. This is often reported as Hyperpolarizability in relevant calculations. (UNVERIFIED)

A deterministic thermostat algorithm that controls temperature by introducing an extended degree of freedom (a thermostat variable) that dynamically couples to the physical system's kinetic energy. This extended variable evolves according to its own equation of motion, causing the physical system's temperature to fluctuate around the target value in a way consistent with the canonical (NVT) ensemble. It avoids the stochastic elements of Langevin or Andersen thermostats (UNVERIFIED).

Hysteresis, in the context of free energy calculations or sampling along a coordinate, refers to the phenomenon where the results obtained depend on the direction in which a simulation parameter or collective variable is changed (e.g., forward vs. backward transformation). Observing significant hysteresis often indicates insufficient sampling or that the system is not remaining close to equilibrium during the process. Minimizing hysteresis is a key goal in demonstrating convergence for certain free energy methods. (UNVERIFIED)

Magnetic spectroscopy encompasses methods that probe the magnetic properties of matter, typically arising from the intrinsic angular momentum (spin) of electrons and atomic nuclei. Techniques like Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) usually involve applying a strong magnetic field and measuring interactions with microwave or radiofrequency radiation. These methods yield detailed information about structure, dynamics, and electronic environments around magnetic centers. (UNVERIFIED)

• hyperfine spectra tensors ^c
• antiferromagnetic coupling ^c

Lambda-dynamics is a free energy calculation method where the coupling parameter, lambda, is treated as a dynamic variable that evolves in time, just like an atomic coordinate. A fictitious mass is assigned to lambda, and its "motion" along the transformation pathway is simulated, allowing it to sample different intermediate states. For experts, this method can enhance the sampling of the alchemical pathway and provide an estimate of the free energy profile from the distribution of the lambda coordinate. (UNVERIFIED)

A specific clustering quality metric that represents the ratio of the sum of squares between clusters (SSR) to the total sum of squares (SST). A value close to 1 indicates that the clusters are well-separated. The SSR/SST ratio is a measure of the variance explained by the clustering. This is a standard statistical measure. (UNVERIFIED)

Free Energy Perturbation (FEP) is an alchemical method for calculating free energy differences between two states (A and B) by simulating a series of intermediate states that gradually transform A into B. The free energy change between adjacent intermediate states (λ and λ+Δλ) is calculated using the Zwanzig equation, which involves ensemble averaging the energy difference exponentiated. Summing the free energy changes over all intermediate steps yields the total free energy difference between A and B. (UNVERIFIED)

The downhill simplex minimizer, also known as the Nelder-Mead algorithm, is an optimization algorithm used to find the minimum of a function in a multi-dimensional space. It works by evaluating the function at the vertices of a geometric shape (a simplex) and iteratively moving, shrinking, or expanding the simplex towards the minimum. For experts, this algorithm is notable because it does not require the calculation of gradients, making it useful for optimizing complex or noisy functions. (UNVERIFIED)

A category of analysis methods focused specifically on characterizing the structure, dynamics, and properties of the solvent molecules (most commonly water) surrounding a solute molecule within a simulation. This includes examining solvent density and distribution around the solute, analyzing hydrogen bonding networks within the solvent and between solvent and solute, calculating residence times of solvent molecules near the solute, and assessing the overall impact of the solvent on solute behavior. It provides crucial insights into solvation phenomena. (UNVERIFIED)

• hydration analysis ^c
• 3D-mapping analysis ^c
• distribution analysis ^c
• closest solvent analysis ^c
• grid inhomogeneous solvation theory analysis ^c

The unit tail atom is the atom in a residue library that is defined as the "end" of the residue, typically the one that connects to the next residue in a chain. In a standard amino acid, this would be the backbone carbonyl carbon atom. This convention is used by system building programs to correctly link residue units together to form a polymer. (UNVERIFIED)

A type of enhanced sampling parameter that controls a Gaussian accelerated molecular dynamics (GaMD) simulation. These parameters define the upper limit of the standard deviation for the potential energy boost. The Gaussian accelerated MD parameter settings are crucial for controlling the balance between accuracy and enhanced sampling. These are often set in a specific gamd section of the input file. (UNVERIFIED)

This branch of spectroscopy specifically investigates the vibrational motions within molecules – the ways chemical bonds stretch, bend, and twist. Techniques in this area measure the characteristic frequencies (energies) of these vibrations, often using infrared light or laser light scattering (Raman). The resulting vibrational spectrum acts like a molecular fingerprint, revealing structural information and identifying chemical groups. (UNVERIFIED)

• vibrational circular dichroism ^c
• infrared spectra ^c
• pre-resonance raman spectra ^c
• raman spectra ^c

The Simple Point Charge water model, a widely used rigid 3-point water model. It has a slightly different geometry (ideal tetrahedral H-O-H angle) and parameter set compared to TIP3P. SPC is known for its computational efficiency and reasonable reproduction of some structural and dynamic properties of water. (UNVERIFIED)

The computational procedure within surface potential analysis used to determine the electrostatic potential generated by the molecule's charge distribution (nuclei and electrons) at specific points in space. This potential is typically calculated using the molecule's wavefunction or electron density and visualized on a surface to reveal its electrostatic character. The results are valuable for predicting intermolecular interactions and reaction sites. (UNVERIFIED)

A crystal lattice environment is a highly ordered, solid-state simulation context where molecules are packed into a rigid, repeating three-dimensional array governed by a specific crystallographic space group. This represents the macroscopic state of a molecular crystal. For structural biologists and simulation experts, this environment is used to simulate X-ray crystallography conditions, study crystal packing forces, or investigate solid-state material properties. (UNVERIFIED)

A unit which is a standard measure of the amount of matter/energy of a physical object.

A beta sheet is a common shape in proteins where parts of the amino acid chain line up side-by-side like ribbons in a flat, pleated sheet. It is a secondary structure motif formed by two or more extended polypeptide chains, called beta-strands, which are linked laterally by a regular pattern of hydrogen bonds between their backbone atoms. These sheet structures form the rigid core of many proteins and are critical for creating binding surfaces for other molecules. (UNVERIFIED)

• anti-parallel beta sheet ^c
• parallel beta sheet ^c

A step within the preparation or equilibration phase where the system's temperature is gradually raised or adjusted to the desired target temperature for the production simulation. This is typically done by coupling the system to a thermostat while velocities are assigned or rescaled. Proper thermalization ensures the system reaches the correct kinetic energy distribution before equilibration or production runs. (UNVERIFIED)

A force calculation algorithm is the computational engine of a molecular dynamics simulation, responsible for determining the forces acting on every atom at each time step. These algorithms compute forces by taking the derivative of the potential energy function defined by the force field, which includes terms for bonds, angles, and non-bonded (van der Waals and electrostatic) interactions. Because calculating the non-bonded forces between all pairs of atoms is the most computationally intensive part of the simulation, specialized methods like Particle Mesh Ewald (PME) are used to perform this step efficiently. (UNVERIFIED)

• electrostatic interaction algorithm ^c
• Treecode algorithm ^c

Ligand Gaussian accelerated molecular dynamics is a specific application of the GaMD method focused on enhancing the sampling of a ligand's movement and conformational changes. The boost potential is applied in a way that specifically accelerates the dynamics of the ligand, its binding site, or both. For experts, this method is a powerful tool for exploring ligand binding pathways and estimating binding free energies. (UNVERIFIED)

• dual-boost ligand Gaussian accelerated molecular dynamics ^c
• ligand Gaussian accelerated molecular dynamics 3 ^c

An earlier force field parameter set from the CHARMM family, notable for being a 'united-atom' force field for proteins. In this representation, nonpolar hydrogen atoms (e.g., on CH, CH2, CH3 groups) are implicitly included in the heavy atoms they are attached to, reducing the number of particles and computational cost compared to all-atom models. It is less commonly used today for high-resolution studies. (UNVERIFIED)

The aug-cc-pCVTZ basis set provides a triple-zeta quality description augmented with both diffuse functions ('aug-') and tight core-correlating functions ('-CV'). This large basis set is designed for high-accuracy calculations where describing core-valence correlation and effects requiring diffuse functions (like anion stability or intermolecular interactions) are simultaneously important. (UNVERIFIED)

A standard text-based file format designed for exchanging NMR-derived information, particularly structural restraints like distances and angles. It provides a standardized way to represent experimental data used for structure calculation and simulation refinement. (UNVERIFIED)

A unit of concentration which expresses a concentration of 1 mole of solute per liter of solution (mol/L).

The cein format is a specialized input file used for simulations that model the gain and loss of electrons by molecules. It defines the properties of residues that can exist in different oxidation states, such as a cysteine that can be oxidized or reduced. This file provides the necessary parameters for a constant redox potential simulation, allowing the system to dynamically change its electronic state in response to a defined electrochemical potential. (UNVERIFIED)

A type of output data descriptor that describes the motion and time-evolution of a system. These properties are directly related to the movement of atoms and molecules, as opposed to their static structure. They are calculated from the time-series data in a simulation trajectory. These properties are often calculated from trajectory analysis of MD simulations. (UNVERIFIED)

• mean square displacement ^c
• REMD round-trip time ^c
• DNA-bendability ^c
• NMR relaxation time ^c
• correlation time ^c
• conformational transition ^c
• rotational diffusion ^c
• mean solvation force ^c
• lifetime curve data ^c
• residence times ^c
• diffusion coefficient ^c

A type of enhanced sampling parameter that controls an umbrella sampling simulation, where a biasing potential is used to confine the system to specific windows along a reaction coordinate. These parameters define the location and strength of the biasing potential in each window. The umbrella sampling parameter settings are essential for setting up simulations to calculate a potential of mean force. These are often set in the input file for each window. (UNVERIFIED)

• umbrella anchor position ^c
• umbrella sampling restraint energy constant ^c
• number of umbrella sampling windows ^c

The aug-cc-pVTZ basis set adds a set of diffuse functions to the standard triple-zeta correlation-consistent basis (cc-pVTZ). This augmentation provides a much better description of electron distribution far from the nuclei, essential for anions, weak interactions (like hydrogen bonds or dispersion), and electronic properties like polarizabilities, compared to the unaugmented cc-pVTZ. It is a widely used standard for high-accuracy calculations requiring diffuse functions. (UNVERIFIED)

Metatwist is an analysis tool for studying the twisting motions of helical molecules, such as DNA, using data from a metadynamics simulation. It is probably designed to analyze a free energy surface calculated as a function of a helical twist collective variable. This would allow a researcher to quantify the energetic cost and identify the pathways associated with the twisting and untwisting of a molecular helix. (VERY-) (UNVERIFIED)

A residue name is a standardized short code, typically three or four letters, used in structure files to identify a specific type of molecular building block. For example, 'ALA' is the residue name for the amino acid alanine, and 'DG' can represent a deoxyguanosine nucleotide.

• modified amino acid residue name ^c
• GLYCAM residue name ^c

The stage of a biomolecular simulation process where the main simulation runs are performed according to the prepared system and defined parameters to generate trajectory data. This phase involves propagating the system forward in time using algorithms like molecular dynamics or Monte Carlo, under specific ensemble conditions. The goal is typically to sample conformational space, observe dynamic events, or calculate specific properties like free energies. (UNVERIFIED)

• umbrella sampling ^c
• production ^c
• free energy calculation ^c
• adaptive steered molecular dynamics ^c

GROMACS typically saves trajectories in binary formats: either .xtc which uses lossy compression for coordinates only, offering significant space savings, or .trr which stores coordinates, velocities, and forces at full precision. The choice between them depends on the required accuracy and data for subsequent analysis. Both capture the time-dependent evolution of the simulated system. (UNVERIFIED)

• trr trajectory format ^c
• xtc trajectory format ^c
• tng trajectory format ^c

A type of structural property that measures the surface area of a molecule that is accessible to a solvent. This quantity is crucial for understanding solvation effects. It is a key component in implicit solvent models and is often used to characterize a molecule's exposure to its environment. This value is commonly known as Solvent Accessible Surface Area or SASA. (UNVERIFIED)

A specialized text-based file format used by the TINKER software package. While it shares the '.xyz' extension with the standard Cartesian coordinate format, it is distinct in that it explicitly includes atom indices, force field atom types, and connectivity (bond) lists for every atom, serving as both a coordinate and topology file. (UNVERIFIED)

A direct dipolar coupling restraint simulation is a method that incorporates experimental NMR data from residual dipolar couplings (RDCs) to guide a simulation. RDCs provide information about the orientation of chemical bonds relative to an external magnetic field. For experts, RDC restraints are extremely powerful for refining the long-range structure and dynamics of a molecule in solution. (UNVERIFIED)

Visual Molecular Dynamics, or VMD, is a computer program for viewing and animating molecules in 3D. As a type of visualization tool, VMD is a high-performance molecular graphics program designed for the visualization and analysis of large biomolecular systems and simulation trajectories from packages like NAMD and GROMACS. It includes powerful atom selection syntax, rendering capabilities for publication-quality images, and a Tcl/Python scripting interface for automating complex analysis and visualization tasks. This tool is commonly known as "VMD" and is associated with file formats like .vmd for saved states and analysis scripts written in Tcl. (UNVERIFIED)

A distance collective variable is a simple coordinate that measures the separation between two specific atoms or groups of atoms. It is one of the most common variables used in simulations to track processes like a drug molecule unbinding from its target protein. Monitoring this distance provides a straightforward way to follow the progress of an association or dissociation event. (UNVERIFIED)

• difference of center of mass distances collective variable ^c
• linear combination of distances collective variable ^c
• center of mass distance collective variable ^c

Ligand analysis is a broad category of methods focused on characterizing the behavior of a small molecule, or ligand, during a simulation of its complex with a larger receptor. This includes analyzing the stability of its binding pose, its internal flexibility and conformational changes, and its specific interactions with the protein or nucleic acid. These analyses are fundamental to structure-based drug design for understanding the determinants of binding affinity and specificity. (UNVERIFIED)

The molecular termini are the distinct starting and ending points of a biological polymer chain, such as the N-terminus and C-terminus of a protein. These regions are chemically distinct from the rest of the chain and often possess unique electrical charges or chemical modifications. For experts, the correct definition of termini (charged/zwitterionic vs. neutral/capped) in the topology is critical for avoiding artificial electrostatic artifacts, especially in short peptides. (UNVERIFIED)

A type of statistical property that estimates the standard deviation of the sample mean, quantifying how precisely the sample mean represents the true population mean. It is calculated by dividing the sample standard deviation by the square root of the sample size. The standard error of the mean is a key measure of the uncertainty of a calculated average value. This is often abbreviated as SEM. (UNVERIFIED)

A general term for algorithms designed to solve systems of linear equations that arise from geometric constraints in molecular simulations, particularly when constraints are applied before integrating equations of motion (e.g., in Lagrangian multiplier methods). While iterative methods like SHAKE/RATTLE solve non-linear equations implicitly, linear solvers might be used in different formulations. It represents the mathematical task underlying some constraint methods (UNVERIFIED).

MDposit is a web-based platform and portal designed for the sharing, visualization, and analysis of molecular dynamics simulation data. It serves as a distributed database interface that allows users to browse, access, and interactively view trajectories from different research groups. This tool aims to facilitate the dissemination and reuse of large-scale simulation datasets within the scientific community. (UNVERIFIED)

JSmol is an open-source, HTML5/JavaScript-based molecular viewer that allows for the interactive 3D visualization of chemical structures within web browsers without requiring Java or other plugins. It is the modern, JavaScript implementation of the popular Jmol applet, widely used in chemical education, databases, and web-based cheminformatics tools. (UNVERIFIED)

A specific type of correlation coefficient that measures the monotonic relationship between two variables, based on their ranks rather than their raw values. It is less sensitive to outliers than the Pearson correlation. The Spearman rank correlation coefficient is a non-parametric measure of association. This is often reported as rho or Spearman's rho. (UNVERIFIED)

Replica-exchange molecular dynamics (REMD), also known as parallel tempering, is an enhanced sampling technique that runs multiple simulations (replicas) of the same system in parallel, typically each at a different temperature. At regular intervals, attempts are made to swap the current configurations between pairs of replicas running at adjacent temperatures, accepted based on a probability criterion. This allows configurations explored at high temperatures (overcoming energy barriers) to diffuse down to lower temperatures, enhancing conformational sampling. (UNVERIFIED)

• constant pH replica-exchange molecular dynamics ^c
• Gibbs sampling replica exchange ^c
• reservoir replica-exchange molecular dynamics ^c
• multidimensional replica-exchange molecular dynamics ^c
• temperature replica-exchange molecular dynamics ^c
• hybrid solvent replica-exchange molecular dynamics ^c
• replica-exchange self-guided Langevin dynamics ^c
• redox potential replica-exchange molecular dynamics ^c

A data file format used in advanced solvent analysis to describe how the interaction between different types of atoms changes with distance. It stores the mathematical functions, known as pair functionals, that are the core components of integral equation theories like the 3D Reference Interaction Site Model (3D-RISM). These files contain the pre-calculated correlation functions for a pure solvent, which are then used by the 3D-RISM method to determine the solvent structure around a solute molecule. (UNVERIFIED)

Cryogenic electron microscopy (Cryo-EM) is an experimental technique that determines the structure of molecules and complexes by imaging samples rapidly frozen in a thin layer of vitreous (non-crystalline) ice using an electron microscope. Sophisticated image processing techniques are used to average images of thousands or millions of individual particles to reconstruct a high-resolution three-dimensional density map. Cryo-EM is particularly powerful for large, flexible complexes that are difficult to crystallize. (UNVERIFIED)

The potential energy arising from the universal gravitational attraction between objects possessing mass, as described by Newton's law of gravitation. While a fundamental interaction governing celestial mechanics, the magnitude of gravitational forces between atoms and molecules is utterly negligible (many orders of magnitude weaker) compared to electromagnetic forces that dominate interactions at this scale. Therefore, gravitational energy is completely ignored in standard biomolecular simulations. (UNVERIFIED)

Specifies the geometric shape of the simulation cell used under periodic boundary conditions (PBCs), which replicate the central simulation system in three dimensions to mimic a bulk environment and avoid surface effects. The choice of shape (e.g., cubic, truncated octahedron, rhombic dodecahedron) affects the computational efficiency (volume of solvent needed) and how well the unit cell packs space. It determines the distance and geometry for interactions between a particle and its periodic images. (UNVERIFIED)

• rectangular/cubic ^c
• hexagonal prism ^c
• triclinic box ^c
• rhombic dodecahedron ^c
• truncated octahedron ^c

A displacement parameter that measures the translation of a base pair away from the central helical axis along the axis of the base pair's hydrogen bonds. The y-displacement is typically small in canonical DNA structures. This is a standard output of nucleic acid analysis programs. (UNVERIFIED)

The Car-Parrinello induced dipole scheme is an efficient algorithm for simulations with polarizable force fields that avoids the costly iterative calculation of induced dipoles at every step. It treats the induced dipoles as dynamic variables with fictitious masses that evolve in time according to classical equations of motion, driven by the forces from the electric field. This extended Lagrangian approach allows the induced dipoles to remain close to their self-consistent values throughout the simulation, providing a significant performance advantage over iterative methods. (UNVERIFIED)

The van der Waals radius represents the effective size of an atom, defining how closely it can approach another atom before they start to repel each other. It is the radius of an imaginary hard sphere that represents the distance of closest approach for another atom, corresponding to the region where strong Pauli repulsion dominates the weak, attractive van der Waals forces. These radii are fundamental for defining molecular surfaces, checking for steric clashes, and as a basis for the "sigma" parameter in the Lennard-Jones potential used in force fields. (UNVERIFIED)

Represents the energy contribution from interactions that are less dependent on the precise chemical nature or orientation of the interacting groups, such as general Van der Waals attraction (dispersion) and repulsion (excluded volume). These forces act broadly between molecules or parts of molecules, contributing significantly to overall cohesion, packing density, and solvation effects (e.g., the hydrophobic effect is driven by minimizing disruption of water, influenced by non-specific interactions). It contrasts with the energy from specific, directional interactions like hydrogen bonds. (UNVERIFIED)

The LCPO (Linear Combination of Pairwise Overlaps) algorithm is a very fast and analytical method for calculating the solvent-accessible surface area of a molecule. It approximates the surface area by summing the contributions from each atom and correcting for the areas that are buried by neighboring atoms. Because of its speed, the LCPO algorithm is particularly well-suited for calculating surface areas "on-the-fly" during a molecular dynamics simulation. (UNVERIFIED)

Transition Path Sampling (TPS) is a powerful simulation technique designed to study rare transition events between stable molecular states by directly sampling the ensemble of reactive pathways connecting them. Starting with one known reactive trajectory, it uses a Monte Carlo procedure in path space (generating new trial paths from old ones) to explore the set of all possible transition mechanisms without needing predefined reaction coordinates. TPS allows for the calculation of rate constants and detailed mechanistic analysis. (UNVERIFIED)

mdrun is the primary high-performance molecular dynamics simulation engine within the GROMACS software suite. It is the specific executable program responsible for reading the compiled run input file (.tpr), calculating the forces between atoms, and numerically integrating Newton's equations of motion to generate the simulation trajectory. For experts, mdrun is highly optimized for parallel execution across multiple CPU cores and GPUs using domain decomposition and message passing interface (MPI). (UNVERIFIED)

This criterion focuses specifically on the nature and magnitude of the structural changes between a pair of ligands being considered for relative free energy calculations. Ideally, the transformation involves small, localized changes (e.g., adding a methyl group, changing a halogen) rather than large rearrangements or changes in net charge, as smaller perturbations generally lead to more reliable alchemical calculations. (UNVERIFIED)

A specific type of orientation descriptor that represents the angle of rotation of a molecule around a specific unit axis. The SPINANGLE is useful for analyzing spinning motions, such as that of a transmembrane protein helix. This is a specialized analysis output. (UNVERIFIED)

A component of the solvation free energy that represents the energetic contribution from electrostatic interactions between the solute and the solvent. This term captures the favorable interactions of polar groups with the solvent and the cost of creating a cavity in the polar medium. It is a key output of continuum solvent models like Poisson-Boltzmann and Generalized Born. This value is often reported as P_SOLV, EPB, or EGB. (UNVERIFIED)

A commercial molecular modeling and computational chemistry software package featuring an integrated graphical user interface. It provides tools for structure building and visualization, and implements a range of computational methods, including molecular mechanics (MM), semi-empirical methods (like AM1, PM3), Hartree-Fock (HF), Density Functional Theory (DFT), and Møller-Plesset (MPn) calculations. Spartan is widely used in education and research for structure-property relationship studies. (UNVERIFIED)

A type of thermodynamic property that quantifies the total energy of the molecular system based on the interactions between its atoms. The energy is calculated at each step using the force field's potential energy function and the atoms' kinetic energy. Monitoring these energy terms is the primary way to assess the stability and convergence of a simulation, ensuring the system has reached a stable state. Simulation log files from packages like AMBER, GROMACS, and CHARMM frequently report this as ENERGY, Etot, or Total Energy. (UNVERIFIED)

• Van der Waals energy ^c
• angle energy ^c
• PME solvent energy density ^c
• dihedral energy ^c
• bond interaction energy ^c
• improper torsion energy ^c
• electrostatic energy ^c
• restraint energy ^c
• charge transfer energy ^c
• potential energy ^c
• solvent reaction field potential ^c
• normalized PME solvent energy ^c
• dispersion energy ^c
• boost energy ^c
• interaction energy ^c
• QM energy ^c
• polarization energy ^c
• 10-12 H-bond energy ^c
• locally enhanced sampling energy ^c
• book-keeping energy term ^c
• reference energy ^c

Pressure is a thermodynamic property that represents the force per unit area exerted by the particles on the boundaries of the simulation box. It is a key indicator of the system's physical state and is monitored to ensure the simulation has reached the correct density under constant pressure conditions. For experts, this value is calculated from the kinetic energy and the virial of internal forces and is maintained by a barostat algorithm in the NPT ensemble. (UNVERIFIED)

Temperature is a thermodynamic property that measures the average kinetic energy of the atoms and molecules in the simulation. It is the primary indicator of the system's thermal state and is constantly monitored to ensure the simulation is stable and correctly samples the target ensemble. For experts, this value is calculated from the particle velocities via the equipartition theorem and is maintained by a thermostat to correspond to a specific thermodynamic temperature. (UNVERIFIED)

An angle collective variable is a coordinate that measures the angle formed by three specific atoms or groups of atoms during a simulation. This variable is used to monitor hinge-like motions, such as the opening and closing of domains in a protein. By tracking this single value, researchers can simplify the analysis of complex structural rearrangements into an easily understandable motion. (UNVERIFIED)

An electronic lab journal source refers to data, observations, or protocols obtained directly from a digital laboratory notebook system used by a research group. Unlike public databases or formal publications, these sources contain raw, internal research records that document the day-to-day progress and specific conditions of an experiment. Citing this source acknowledges the provenance of data that exists within a private institutional framework and has not yet been publicly deposited or peer-reviewed. (UNVERIFIED)

Binding Free Energy Estimator 2 (BFEE2) is a comprehensive computational workflow designed to calculate protein-ligand binding free energies with high accuracy. It automates a rigorous multi-step process that includes enhanced sampling of the ligand's binding pose and the use of alchemical free energy methods to compute the final affinity. This tool aims to provide a standardized and reproducible protocol for obtaining reliable binding energy predictions that can guide drug discovery projects. (UNVERIFIED)

Intermediate Neglect of Differential Overlap, an all-valence-electron semi-empirical method that is an improvement over CNDO. It retains one-center electron repulsion integrals between orbitals on the same atom, which CNDO neglects, allowing it to better describe electron spin distributions and properties dependent on them. It is computationally slightly more demanding than CNDO but generally more accurate (UNVERIFIED).

An electrostatics analysis tool is a type of software designed to calculate and visualize the electrostatic properties of a molecule. These tools typically take a molecular structure with assigned atomic charges and compute quantities like the electrostatic potential on the molecule's surface or the total electrostatic energy of solvation. They are essential for understanding how a molecule will interact with other charged molecules and its polar solvent environment. (UNVERIFIED)

The extract_LIEenergies.pl script is a utility designed to parse simulation output files and extract the specific energy components required for a Linear Interaction Energy (LIE) calculation. It typically reads the log files to find the average van der Waals and electrostatic interaction energies of a ligand with its environment. For researchers using the LIE method, this script automates the data extraction step needed to calculate the binding free energy. (UNVERIFIED)

A statistical ensemble representing open systems where the chemical potential (μ), the system volume (V), and the temperature (T) are held constant; hence often called the μVT ensemble. The system can exchange both energy (with a heat bath at T) and particles (with a particle reservoir at chemical potential μ). Simulations in this ensemble are useful for studying systems where the number of particles can change, such as adsorption phenomena, phase equilibria (vapor-liquid), or systems involving chemical reactions where concentrations are fixed rather than particle numbers. (UNVERIFIED)

ROCS (Rapid Overlay of Chemical Structures), a software tool developed by OpenEye Scientific Software, known for its speed and effectiveness in aligning and comparing molecules based on their 3D shape similarity (shape Tanimoto). ROCS represents molecules as Gaussian functions and optimizes their overlap to quantify shape similarity, often used in virtual screening and lead hopping in drug discovery to find molecules with similar shapes to a known active ligand. It is a similarity calculation tool, not directly a TI tool. (UNVERIFIED)

• thermodynamic integration similarity calculation tool ^c
• match analysis tool ^c

An information content entity that is the outcome of a dubbing process and is used to refer to one instance of entity shared by a group of people to refer to that individual entity.

• denotes ^op some
  
• is_specified_output_of ^op some
  

A potential of mean force is an energy profile that shows how much energy it takes to move a molecule from one place to another. As a type of free energy, the Potential of Mean Force (PMF) is an output_data_descriptor that represents the free energy of a system as a function of one or more specific geometric coordinates, known as reaction coordinates. The PMF describes the energetic landscape along a pathway, with its minima representing stable states and its maxima corresponding to transition state energy barriers. This is commonly referred to in analysis outputs and publications as "PMF," "free energy profile," "Potential of Mean Force," or "pmf.dat." (UNVERIFIED)

Refers to the dynamic transformations or fluctuations observed in the secondary structure elements of a biomolecule during a simulation or over time. Monitoring these changes, such as the formation or dissolution of helices or sheets, provides insights into molecular flexibility, folding pathways, or responses to interactions. Analyzing these dynamics helps understand how molecular function relates to structural transitions (UNVERIFIED).

The swarm-of-trajectories approach refers to computational strategies that utilize a large number of independent, often relatively short, molecular dynamics simulations launched from specific initial conditions. This "swarm" allows for efficient statistical sampling of pathways, transition probabilities between states, or average forces needed in methods like the String Method or Milestoning. It contrasts with relying on a single, very long trajectory to observe events of interest. (UNVERIFIED)

Refers to a modified set of Bondi radii, where adjustments have been made to the original Bondi values, often for specific atom types or elements, to improve performance in particular applications within molecular simulation software (the prefix 'm' often stands for 'modified'). For example, in the AMBER software package, 'mbondi' radii sets might involve different radii for hydrogens depending on the atom they are bonded to, optimized for better agreement between calculated and experimental solvation free energies when used with specific GB models. The exact definition can vary between different 'mbondi' versions (e.g., mbondi, mbondi2, mbondi3). (UNVERIFIED)

A data format defines the specific rules and conventions used to structure, store, and exchange data, particularly within computer files. In biomolecular simulation, this refers to the various standardized ways that information like molecular structures, simulation parameters, or results are organized. Understanding these formats is essential for using simulation software and sharing data. (UNVERIFIED)

• volumetric data format ^c
• NMR data format ^c
• general data format ^c
• molecular data format ^c
• sequence data format ^c
• plot data format ^c

Specific versions 2 of the OPEP (Optimized Potential for Efficient peptide structure Prediction) coarse-grained force field. OPEP represents each amino acid residue using multiple beads (typically backbone N, H, Cα, C, O and a side-chain bead), aiming to retain chemical specificity while gaining computational efficiency. The different versions likely represent successive refinements and parameter updates. (UNVERIFIED)

UCSF ChimeraX is the next-generation molecular visualization and analysis program developed by the Resource for Biocomputing, Visualization, and Informatics at UCSF. It is designed to handle extremely large datasets, such as cryo-EM maps and massive simulation trajectories, with high-performance rendering. In addition to visualization, it serves as a powerful modeling and setup tool, offering capabilities for structure building, fitting, and interactive manipulation. (UNVERIFIED)

• structure preparation tool ^c
• molecular structure visualization tool ^c

Reservoir replica-exchange molecular dynamics is an efficient variant of the REMD method for simulations with a very large number of replicas. Instead of attempting swaps between all adjacent pairs, it attempts swaps between a master simulation and a large "reservoir" of simulations running at different temperatures. For experts, this can significantly improve the efficiency of the exchange process when a very wide temperature range needs to be sampled. (UNVERIFIED)

A GROMACS include topology file (.itp) contains the topology definition for a specific type of molecule (like a protein, lipid, or solvent). It typically includes sections like [ moleculetype ], [ atoms ], [ bonds ], etc., and is designed to be reusable. These .itp files are incorporated into the main system topology (.top) file using the #include directive. (UNVERIFIED)

Refers to the specific condition or status of a ligand molecule, particularly in the context of its interaction with a receptor molecule (like a protein). This encompasses various aspects, including whether it is bound or unbound, its specific binding pose or conformation, its protonation or tautomeric form, and its electronic state. Characterizing different ligand states is fundamental to understanding molecular recognition and drug action. (UNVERIFIED)

• solvated state ^c
• unbound state ^c
• transition state ^c
• encounter complex ^c
• protonation state ^c
• tautomeric state ^c
• conformational state ^c
• bound state ^c
• metastable state ^c
• excited state ^c

An optimization algorithm is a procedure that systematically searches for the best possible solution from a set of available alternatives, typically by finding the input values that result in the minimum or maximum of a given function. In molecular simulation, these algorithms are used to find the lowest energy conformation of a molecule or to determine the most likely transition pathway. For experts, the choice of optimization algorithm can greatly affect the efficiency and success of finding a solution. (UNVERIFIED)

• SCF convergence algorithm ^c
• Powell's algorithm ^c
• Broyden-Fletcher-Goldfarb-Shanno algorithm ^c
• energy minimization algorithm ^c
• transition state search algorithm ^c
• Levenberg-Marquardt algorithm ^c

ATLAS is a specialized database that stores a comprehensive collection of standardized all-atom molecular dynamics simulations of proteins. It combines simulation trajectories with analyses of protein flexibility and dynamics, linked to experimental structural data. This resource allows researchers to explore the dynamic properties of a wide range of protein families in a consistent and comparative manner. (UNVERIFIED)

An average structure calculation is a structural analysis method that computes the average coordinates of all atoms over a simulation trajectory. This provides a single, representative structure that reflects the central conformation of the system during the simulation. For experts, it is important to note that this average structure may not be a physically realistic conformation itself, especially if the molecule is highly flexible. (UNVERIFIED)

The process of creating graphical representations of molecular structures, trajectories, and simulation data using specialized software. Visualization is essential for inspecting system setup, monitoring simulation progress, understanding molecular motion and interactions, identifying structural features, and communicating results effectively through images and animations. It is an integral part of both preparation and analysis stages. (UNVERIFIED)

The GROMACS rtp format is a text file that acts as a database entry for a molecular building block, such as an amino acid. It defines the atoms, their charges, and their bonding within a specific residue, and is used by the GROMACS software to automatically construct the topology for a polymer like a protein. These residue topology files (.rtp) are a core part of a GROMACS force field and work together with other files to define the complete molecular model. (UNVERIFIED)

The espgen.py script is a utility used to generate the grid of points around a molecule where the electrostatic potential (ESP) will be calculated by a quantum chemistry program. This grid is a necessary input for deriving ESP-fitted atomic charges, such as RESP charges. For researchers parameterizing a new molecule, this script automates a key step in the charge-fitting process. (UNVERIFIED)

A subset of reaction analysis that uses the positions (coordinates) of atoms to describe the progress of a chemical reaction or conformational change. It defines one or more geometric variables, collectively known as reaction coordinates, to map the transition pathway between different molecular states. This analysis helps visualize and quantify the structural changes during a reaction. (UNVERIFIED)

• intrinsic reaction coordinate analysis ^c
• direct reaction coordinate analysis ^c

A theoretical approach is the set of fundamental scientific principles or mathematical ideas used to explain a phenomenon. As a type of method, it represents the underlying physical theory, such as quantum mechanics or empirical method, upon which a specific computational method is built. This choice dictates the fundamental equations and approximations used, for example, distinguishing between a first-principles ab initio calculation and a classical molecular dynamics simulation. This concept is typically described in publications using phrases like "level of theory," "theoretical framework," "ab initio," "semi-empirical," or "classical mechanics." (UNVERIFIED)

• ab-initio method ^c
• inhomogeneous fluid solvation theory ^c
• empirical method ^c
• quantum mechanics ^c

The Gaussian log file (.log) is the standard text output generated by the Gaussian quantum chemistry software suite. It contains a detailed, often verbose, record of the calculation, including setup information, convergence progress for SCF and geometry optimizations, final energies, molecular orbital details, calculated properties (like dipole moments, charges), and often vibrational frequencies and thermochemical analysis. A compact summary, the "archive entry", is usually included near the end. (UNVERIFIED)

Stiffness is a property that describes a molecule's resistance to being deformed by an external force. In simulations, this can refer to the rigidity of a specific bond or angle, which is determined by its force constant in the force field. It can also refer to a collective property of a larger structure, quantifying the energetic cost of large-scale bending or stretching motions. (UNVERIFIED)

A type of kinetic property that measures the average distance a particle has traveled from its starting position over a certain time interval. The Mean Square Displacement is a key quantity used to characterize the dynamics of a system. The slope of the MSD curve over time is directly proportional to the diffusion coefficient. This is often abbreviated as MSD. (UNVERIFIED)

An anisotropic position scaling barostat is a pressure control algorithm that allows the lengths of the three simulation box vectors to fluctuate independently to maintain a constant pressure tensor. This allows the shape of the simulation box to change, which is necessary for simulating systems that are not uniform in all directions, such as lipid membranes or solid crystals. For experts, this method is essential for studying phase transitions or materials under non-uniform stress. (UNVERIFIED)

A computational tool specifically designed to generate realistic initial configurations of lipid bilayers, often including embedded proteins, for use in membrane simulations. These tools arrange lipid molecules (and potentially cholesterol, solvent) according to specified lipid types, compositions, and area per lipid, ensuring proper packing density and avoiding steric clashes, which is challenging to do manually. Examples include PACKMOL-Memgen, CHARMM-GUI's Membrane Builder, and InflateGRO. (UNVERIFIED)

• InflateGro ^c
• MemProtMD ^c
• AMBAT ^c
• PACKMOL-Memgen ^c
• CHARMM-GUI ^c

A CHARMM-specific format that contains the numerical force field parameters, such as force constants and equilibrium values for bonds and angles. It provides the energy constants that correspond to the atom types defined in a residue topology file (RTF). (UNVERIFIED)

A specific type of correlation function that measures the covariance of a signal with itself at different time lags. It is similar to the autocorrelation function but is not normalized. The auto-covariance is a fundamental concept in time-series analysis. This is a standard output of time-series analysis packages. (UNVERIFIED)

A QM/MM switching function is a mathematical tool used in advanced simulations to create a smooth transition zone between the high-accuracy quantum region and the simpler classical region. In adaptive QM/MM methods, this function smoothly blends the forces and energies from the QM and MM calculations in a "buffer" region, preventing abrupt changes as atoms move between the different levels of theory. The use of a well-designed switching function is essential for maintaining energy conservation and numerical stability in simulations where the QM/MM boundary is allowed to change dynamically. (UNVERIFIED)

A type of statistical property used to evaluate the performance of a clustering algorithm. These metrics provide a quantitative measure of how well the algorithm has partitioned the data into distinct and compact clusters. They are essential for assessing the validity of a clustering result. These are standard outputs of clustering analysis programs. (UNVERIFIED)

• SSR/SST ratio ^c
• Davies-Bouldin Index ^c
• pseudo-F statistic ^c
• cluster silhouette ^c

A free energy surface analysis tool is a software utility used to reconstruct the multidimensional free energy landscape of a system from enhanced sampling simulation data. It processes the history of visited states or applied biases, such as those from metadynamics or umbrella sampling, to generate a potential of mean force (PMF) map. For experts, these tools enable the visualization of low-energy basins and transition barriers along specific collective variables or reaction coordinates. (UNVERIFIED)

Wavelet analysis is a sophisticated dynamics analysis technique used to study time-series data where the frequency content is changing over time. Unlike a standard Fourier transform, a wavelet transform can reveal both the frequency of a motion and the time at which it occurred. For experts, this method is a powerful tool for analyzing complex molecular motions, such as identifying transient conformational changes or intermittent dynamic events in a simulation trajectory. (UNVERIFIED)

A type of statistical property that measures how far two subsets of a metric space are from each other. It is the greatest of all the distances from a point in one set to the closest point in the other set. The Hausdorff distance is a robust metric for comparing the overall shape of two conformational ensembles. This is a specialized metric in topology. (UNVERIFIED)

A statistical analysis parameter that specifies the total number of times the original data is randomly resampled during a bootstrap analysis. A larger number of bootstrap replications improves the stability and reliability of the estimated uncertainty. This is a key parameter for controlling the robustness of the bootstrap analysis. This is often set to a value of 1000 or more. (UNVERIFIED)

The General AMBER Force Field (GAFF), designed as a companion to the main AMBER biomolecular force fields (for proteins, nucleic acids). It provides parameters for a wide range of organic molecules based on atom types determined by chemical environment and bonding patterns, following the same functional forms as the AMBER force field. GAFF is widely used for parameterizing ligands, drugs, and organic cofactors in simulations involving AMBER biomolecular force fields. (UNVERIFIED)

A type of analysis parameter that controls the generation of three-dimensional volumetric data, such as density grids or electrostatic potential maps. These parameters define the size, spacing, and function used to create the grid. The volumetric analysis parameter settings are crucial for visualizing the spatial properties of the system. These are often set in a grid command in an analysis script. (UNVERIFIED)

• grid spacing ^c
• grid function ^c
• grid points ^c

The aug-cc-pCV6Z basis set represents one of the largest available standard basis sets, combining a sextuple-zeta description with functions for both core-valence correlation ('-CV') and diffuse character ('aug-'). Its use is restricted to the most demanding benchmark calculations on very small systems aiming for the highest possible accuracy in treating both core and diffuse electron effects concurrently. (UNVERIFIED)

The second generation of the General AMBER Force Field (GAFF2), representing an update and refinement of the original GAFF. Released around 2015, GAFF2 incorporates more parameter types derived from fitting to higher-level quantum mechanical data, aiming to improve accuracy and coverage for a diverse range of organic molecules. It maintains compatibility with contemporary AMBER biomolecular force fields. (UNVERIFIED)

An ion placement method is a specific procedure used during system setup to add ions, such as sodium or chloride, to the simulation box. The primary purpose is usually to neutralize the total charge of the system and to mimic a specific salt concentration. For experts, the choice of method can be important, as placing ions in physically reasonable locations based on electrostatics is preferred over random placement. (UNVERIFIED)

• ion concentration calculation analysis ^c
• ion randomization analysis ^c
• Laplacian mapping ion placement analysis ^c

A directive information entity with action specifications and objective specifications as parts, and that may be concretized as a realizable entity that, if realized, is realized in a process in which the bearer tries to achieve the objectives by taking the actions specified.

• has part ^op some
  
• has part ^op some
  

• algorithm ^c
• software ^c

A type of thermodynamic property that measures the amount of work obtainable from a system at constant temperature and pressure, determining the spontaneity of a process. It combines both enthalpy and entropy, making it a key predictor of stability and binding affinity. Calculations often result in a Free Energy difference, which is a primary result of many advanced simulation studies. This quantity is often denoted as ΔG or delta G. (UNVERIFIED)

• helmholtz free energy ^c
• potential of mean force ^c
• solvation free energy ^c
• relative binding free energy ^c
• excess chemical potential ^c
• gibbs free energy ^c
• binding free energy ^c