Questions tagged [molecular-dynamics]

For questions related to the use of or theory behind classical or ab initio molecular dynamics.

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2
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0answers
18 views

Rule of Mixtures calculation

I do not understand a part from rule of mixtures.Particularly between upper bound elastic modulus and lower bound elastic modulus calculations I seriously do not understand what value to choose based ...
7
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14 views

Lone Pairs in CHARMM for MD

I have a substrate that has a Br-C bond. In CHARRM the line below is included in the .str file: ...
7
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1answer
67 views

cp2k conserved quantity changed when restart NVT MD?

The details are descripted elsewhere, but got no answer for days, so I post it here for help. As title said, I noticed a relatively big change in conserved quantity and don't know why. I've upload ...
13
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1answer
181 views

Compute RDF between COMs of two selections (or groups) using GROMACS

I have been using gromacs since years but I am always confused when I want to perform the following task: compute the RDF (radial distribution function) between the ...
11
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61 views

Recent developments in QM/MM for Molecular Dynamics

I am looking for new QM/MM methodologies which have recently developed and implemented into MD packages. Any applications or molecular systems studies with these methods can be used as an example as ...
10
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62 views

Using Molecular Dynamics as an experimentalist to study how much plastic work is converted to heat, does anyone have any comments on our paper?

When you load a metal and the deformation results in permanent plastic deformation, the input work should be converted into heat and thus dissipate. But for about 100 years people have struggled to ...
14
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1answer
140 views

Visualizing MD generated electron density cubes as trajectories

During an ab-inito MD simulation one can generate the electron density cube file which basically provides the electronic density data in a standard volumetric format as shown here. The file consists ...
8
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44 views

Periodic polarizable QM/MM embedding

Are there any standalone open source software codes available for periodic polarizable QM/MM embedding MD simulations? In my knowledge, CP2K only has the option for electrostatic embedding and other ...
7
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54 views

How to effectively simulate high density systems in GROMACS?

I have a system with a dense liquid solvent and a polymer solute. I have inserted all the molecules randomly using gmx insert-molecules and then did the energy minimization and equilibration steps to ...
9
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0answers
36 views

Algorithmic description of implementing path integral molecular dynamics?

Suppose I have a functioning molecular dynamics package for classical MD. I want to extend this code to run path integral MD. I know that a surprisingly small number of new features need to be ...
4
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0answers
47 views

Are there other kinds of stability of materials? How to demonstrate that with computation approaches?

I have known some kinds of stability of materials, such as: Mechanical stability; Dynamical stability; Thermal stability In particular, they can be studied with first-principles computational ...
8
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1answer
57 views

For ergodicity, what is the significance of the R value and slope?

I am calculating MSDs for the first time and have been struggling to find newbie-level resources on understanding them. If anyone could please suggest any resources or provide guidance on how to ...
6
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60 views

How to build amorphous Al2O3 using the AIMD method implemented in VASP?

I want to build amorphous Al$_2$O$_3$ with the AIMD (ab-initio molecular dynamics) method implemented in VASP. I know that two procedures should be taken into account, namely 1st: melt 2nd: quench ...
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28 views

How can I quantify the uncertainty of thermal molecule properties in molecular dynamics simulations?

When doing molecular dynamics simulations, there are countless sources of error (i.e. approximations and numerics). Molecular dynamics can be used to determine intrinsic thermal properties such as ...
9
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1answer
69 views

Methods to handle non-ergodic systems with Molecular Dynamics

Given the large difference between simulation timescales and the timescales on which we normally interact with ensembles of molecules, the time average of a molecular dynamics simulation does not ...
9
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1answer
251 views

Classical Monte Carlo vs. Molecular Dynamics

Both Classical Monte Carlo (MC) and Classical Molecular Dynamics (MD) simulations are used to perform simulations of ensembles of molecules. These MC calculations are calculating thermodynamic ...
7
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1answer
82 views

Do we have specific benchmarks for the speed of a simulation of an empty water box with different water models?

I'm looking for a simulation of different water models (TIP3P, SPC/E, TIP4P, water models with flexible bounds) where the differences in simulation speeds on a common architecture are really seen. ...
10
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1answer
64 views

Is there a way to understand pi-pi interactions through GROMACS?

I have two polymer molecules with benzene rings as a part of them. I would like to understand how the interactions between them influences the solvability of the polymer in a non-aqeous solvent. I ...
8
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38 views

Reaction simulation at specific temperature, pH and pressure [closed]

Can we design metal organic frameworks, layered double hydroxide using LAMMPS? How? I want to synthesize a metal organic framework or such materials, and I want to ask if I put two to three chemicals ...
8
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1answer
53 views

Generating topology for charged molecules

I have to generate a topology file for a molecule like Sodium Triphosphate, and I do not find forcefields available in the literature. So as a starting point would like to use engines like LigParGen ...
10
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1answer
132 views

Why does my calculation using GROMACS get stuck at step 0?

I have been using the HPCE on our campus for MD simulations using GROMACS. However, when I use the following script, after the job starts to run on the cluster, gets stuck at Step 0 in the log file. <...
8
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1answer
54 views

What is the state-of-the-art in current flexible water models?

Do we have water models so far which are flexible? How good can they model specific properties of water and are they currently used with force fields and in actual simulations?
6
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1answer
65 views

Is it possible to simulate the Raman spectra via Molecular Dynamics (MD) using the GROMACS package?

I'm new to molecular dynamics and DFT. The aim was to study the Raman spectra of a molecule in a medium. As we know the Raman spectra of a molecule change due to the induced polarization in the ...
9
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1answer
137 views

Computational biology textbook similar to “Computational Materials Science” by June Gunn Lee

I'm looking for a text for computational biology which is similar in structure to a book called Computational Materials Science by June Gunn Lee. In his book, Lee discusses the theory of MD ...
10
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2answers
71 views

Choosing RAM, CPU time, # of cores, and other parameters for an MD run

I did an AIMD run in VASP using 64 cores (32 cores/node) and 250 GB of memory (125 GB/node) for 5 ps (1 fs time step). The calculation took 12.6 hours to complete. CPU efficiency was 99.7% and memory ...
14
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1answer
83 views

How exactly does one compute the vibrational density of states from the output of a molecular dynamics simulation?

There are many things that can be done with the output of a molecular dynamics simulation, but one of the more powerful things is the ability to compute the vibrational density of states (or the ...
11
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91 views

Empirically determining thermostat damping factor

tl;dr Is there a way to determine an appropriate thermostat damping factor given a timestep size and a numerical integration method? I am computing a set of simulations in LAMMPS, using ReaxFF, ...
18
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2answers
722 views

Why do people care about reversibility in molecular dynamics simulations?

When carrying out a molecular dynamics simulation, one has to choose an ensemble. Depending on the problem, one usually works in the microcanonical (NVE), canonical (NVT), or grand canonical ensemble (...
7
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1answer
64 views

Software recommendations for peptide conformation

I have a series of alanine dipeptide trajectories and would like to get the conformation type ($\alpha$, $\beta$, etc.) from the atom coordinates or dihedral angles. Does any package (like RDKit for ...
8
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1answer
53 views

Finding conformations of peptide based on dihedral angles

I was trying to look at the alanine dipeptide trajectories from this link and track the trajectories in a Ramachandran plot. Below is a plot based on dihedral angles at each timestep for all ...
15
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50 views

Benchmark Timings of Machine Learning Potentials vs Molecular Mechanics Force Fields

Machine learning is an increasingly common tool for developing force fields for molecular dynamics simulations. It's not totally clear what should be considered a machine-learning potential, but let's ...
7
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1answer
71 views

Dihedral angles of alanine dipeptide

I have a number of trajectories of alanine dipeptide molecule and I'm interested in computing dihedral angles of each configuration. $\quad\quad\quad\quad$ Have I selected the right atoms for ...
9
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0answers
64 views

Equilibration of normal modes in water molecule [closed]

When running a molecular dynamics simulation on a singular water molecule in vacuum to analyze its normal modes of vibration from the NVE (microcanonical) ensemble, the bending mode frequency is ...
9
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2answers
124 views

Tools for structural analysis on LAMMPS trajectories

I have a very general question but still quite important since I didn't find convincing tools to get the structural analysis done for LAMMPS dump file (trajectories). I am looking for post processing ...
9
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2answers
53 views

Evaluating the MSD of my simulation

I am running a molecular dynamics simulation of water in TIP3P, and I am storing the positions of my particles in a 2D array called relevant_positions. The number ...
11
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1answer
107 views

How does one compute the boiling point of a liquid made of a particular molecule?

This question is in relation to Anomalous boiling point of "iso-" alkanes on Chemistry SE. I want to compute the boiling point of the different isomers of an n-carbon alkane to check what ...
8
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1answer
121 views

How to calculate the orthogonal representation of a HCP cell?

I'm trying to write a program to calculate the neighbor lists of crystal systems. I found a few codes that are able to calculate it for orthogonal systems. How can I do it for non-orthogonal cells ? ...
10
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2answers
125 views

Algorithm for calculating dielectric constant of water TIP3P

I am running a NVT TIP3P simulation of water with 125 molecules of water in a 16-by-16-16 angstrom box with periodic boundary conditions on LAMMPS, with a time-step of 1 fs for 10 ps. Once the ...
10
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1answer
125 views

AIMD and velocity scaling in VASP

Typically one does velocity scaling to "heat" their sample with MD. How do we do this in VASP? Is it by setting the SMASS=-1 and ...
9
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2answers
81 views

Alanine dipeptide trajectories dataset

I was looking for a dataset of alanine dipeptide trajectories. I was wondering whether there is such dataset available or it is unlikely to find one and I should start running molecular dynamics ...
9
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2answers
121 views

How to build a simulation model for a molecular dynamics simulation

I have got aggregate of 4 non-protein compounds I would submit for molecular dynamics simulation. The problem is I can't find software capable to do that. Amber, GROMACS, LAMMPS, all of them require ...
13
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1answer
87 views

How much of a difference in a protein's radius of gyration can be considered significant?

In molecular dynamics simulations of proteins, the radius of gyration is often used to assess the compactness of a protein. When comparing two protein radius of gyration, what difference can be ...
9
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1answer
100 views

Modelling water using the TIP3P flexible system [closed]

I am modelling water using a TIP3P flexible system. I am using the pair, bond and angle parameters given on the LAMMPS webpage. I am trying to run an $NPT$ simulation at $298\,K$ and $1 \,\mathrm{atm}$...
16
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1answer
149 views

Is there any reason not to sum the kinetic and potential energy from an NPT simulation to get internal energy?

I would be very grateful for some newbie-level advice from a thermodynamics guru. I ran NPT simulations on a particular system (in CP2K software) to get fluid densities for use in fluid dynamics ...
8
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0answers
74 views

Collective variable to determine the number of bonds in the shortest Hydrogen bond wire [closed]

I am trying to program a collective variable in PLUMED which is basically the number of bonds in the shortest Hydrogen bond wire in a system of water molecules. I plan to use the HBond_Matrix from ...
8
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1answer
133 views

Using the VACF command in LAMMPS to get the velocity autocorrelation function

I am writing a simple Lennard-Jones fluid simulation in LAMMPS. So far, I have outputted the temperature, volume, density, total energy, enthalpy, pressure, and all of it seems to be believable every ...
7
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0answers
93 views

How to do molecular dynamics calculations and analyse trajectories of small molecules? [closed]

I need to perform some MD calculations and then trajectories of some small molecules analyzed. What I have is protein cofactor (FAD) small molecule (either single O2 molecule or single Chlorine atom) ...
10
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1answer
147 views

Can I compute the free energy difference in (temporally) nearby micro-states using the Zwanzig equation for Free Energy Perturbation?

I wanted to understand the Free Energy Perturbation in an NVT ensemble. Wikipedia explains it as: $$ \tag{1} \Delta F = F_1 - F_0 = -\kappa T \ln \left<\exp\left( \frac{-(E_1-E_0)}{\kappa T}\right)...
20
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2answers
677 views

Does increasing Lennard-Jones cutoff means higher accuracy?

I am currently trying to simulate a large box of QM/MM water molecules with SPC/Fw model and GGA DFT functional (a cube of 40 angstrom sides). To validate the QM and MM simulations separately, I am ...
12
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1answer
88 views

Modelling Diffusion of Molecules Through a Physical Barrier

I would like to model the diffusion of various small molecules (e.g. $\ce{O2}$, $\ce{H2O}$, $\ce{MeOH}$, etc.) through polymeric barrier material (e.g. polyethylene, ethylene vinyl alcohol, ...