Questions tagged [molecular-dynamics]

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

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6
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0answers
24 views

How do I build and run a simulation of water molecules in NAMD?

So, I have started to learn NAMD because I need that for a project I will be doing in the next couple of months. I have some prior experience of MD with gromacs. I thought that since NAMD has a GUI ...
7
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0answers
28 views

Creating Interatomic Potential for Lammps using DFT

What are the basic steps and methodologies used in creating inter-atomic potential (specially EAM, MEAM potentials) for metals ...
4
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1answer
69 views

Simulating polymers using cellular automata?

I am a physics student, and I am working on my final year project, I am planning to simulate polymers using cellular automata. I am really struggling with this project, if someone can give me any ...
9
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1answer
126 views

How can I calculate the Poisson ratio of an amorphous material with LAMMPS?

I noticed that we can calculate the Poisson ratio of a crystalline metals with LAMMPS. I wonder if we can use that example for a metallic glass! If no, is there any other way, with another software?
7
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70 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 ...
7
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0answers
107 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 ...
9
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0answers
47 views

What kind of physical properties can be calculated from the “Valence Electron Density” data of a molecule?

I'm wondering specifically in the context of calculating physical properties from valence-electron-density data using DFT, MD, and or ML (machine learning).
7
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1answer
109 views

How to address the errors on Automated Topology Builder?

I was trying to get the charges and the topology file for this molecule (C28H58O7S8). But I get the following error despite using the right number of hydrogens. Error: Semi-empirical geometry ...
11
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1answer
98 views

Selection of appropriate Langevin damping parameter for MD of solid metal

I am performing an MD simulation involving solid metal. The system is in the NVT ensemble, and I am using the Langevin thermostat (fix Langevin in LAMMPS) to enforce this. I have previously used the ...
12
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1answer
52 views

What does this temperature & total free energy profile mean (obtained from VASP NVT molecular dynamics simulations)?

In order to obtain molecular dynamics (MD) simulations trajectory for computing phonon dispersion relation at finite temperature, I performed NVT MD simulation using VASP for my target system. Here is ...
14
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2answers
239 views

What are the parameters that need to be calculated to design the structure of a molecule?

Before performing Molecular Dynamics on a co-polymer that doesn't have a ready-to-use structure anywhere, the monomer fragment was built in Avogadro software with 0 net charge, B3LYP theory and 6-31G(...
4
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0answers
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Can we calculate the intermembrane protonation state?

I want to know the protonation state of the intermembrane subunit of a protein. For that, I need to know the pH, so given that small molecules can cross the lipid bilayer, could we assume intracelular ...
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6answers
2k views

How do I simulate the interaction between two atoms?

I want to build a rough atom interaction simulator, where pushes two (or more) atoms toward each other and they should behave physically correctly: attract, bond or repel with some force. So that is ...
12
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1answer
91 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 ...
8
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1answer
63 views

Understanding the rigorous bridge between atomistic and coarse-grained simulations

I am currently reading this paper by Noid et. al. on the rigorous bridge between atomistic and coarse-grained simulations. In the paper, he defined a linear map from the atomistic coordinates and ...
9
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0answers
81 views

Is there any code that runs WHAM starting from histograms rather than time series?

I'm looking for a way to run the Weighted Histogram Analsys Method, but I don't have a time series to feed to the code as usually happens, but rather I have histograms coming from the debiasing of a ...
10
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76 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? [closed]

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 ...
7
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1answer
50 views

How to discard molecules at the boundary in the Atomic Simulation Environment (ASE)?

When building a supercell for a molecular crystal with the Atomic Simulation Environment, it seems that the program takes into account periodic boundary conditions when replicating the unit cell. How ...
7
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1answer
46 views

How to calculate the volumetric energy density of a molecule?

I am trying to store hydrogen in a hydrocarbon. The example can be taken as cyclohexane ($\ce{C6H12}$) which is in a hydrogen-rich state. Its hydrogen-lean state is Benzene. I want to calculate the ...
12
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1answer
154 views

Analyzing MD trajectory: molecule orientation

I'm running a MD simulation (in Gromacs) of dye molecules incorporated into polymer to determine how that system responds to external electric field. There are two order parameters that are used to ...
13
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0answers
123 views

Empirically determining thermostat damping factor

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, tracking ...
5
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0answers
90 views

Fix deposit and USER-REAXC: pre-allocating memory for atoms when using LAMMPS with ReaxFF

I would like to use "fix deposit" with ReaxFF to add atoms to a simulation in which I deposit molecules on a surface. I have built working scripts for my system with other force fields. ...
11
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2answers
61 views

What is the most appropriate (and easy-to-use) all-atoms force field for liquid electrolytes?

I need to simulate a salt diluted in a liquid electrolyte. My experience is with LAMMPS, but so far I only had coarse grained toy models, and setting up the force field was straightforward. Now I have ...
13
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1answer
147 views

Minimum image convention for non-orthorhombic unit cells

I am trying to take into account periodic boundary conditions for non-orthorhombic unit cells. I have the atomic coordinates for a monoclinic super cell with the following lattice vectors output by ...
8
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2answers
98 views

Large pressure fluctuations in molecular dynamics

I'm performing MD simulations, using NPT ensemble. The problem is that the pressure fluctuates severely and doesn't average at required level. For example, I set the pressure at 1 bar and it averages ...
6
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1answer
65 views

Molecular dynamics: how to pack system for desired density

I'm trying to perform ab-initio MD on polymer system. I've built single chain of polycarbonate (PC) with the length of ~40 angstroms and now I'm building initial configuration. I've calculated how ...
3
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1answer
31 views

Missing residues in ATB downloaded pdb/rtp files

I have downloaded the diglyme molecule from the ATB server (http://atb.uq.edu.au/molecule.py?molid=34570#panel-md) Two files are available: a PDB file and a topology ITP/RTP file. The name of the ...
13
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2answers
484 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 ...
23
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1answer
137 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 ...
4
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0answers
33 views

What will be the cohesive energy of an alloy in LAMMPS?

The cohesive energy of a pure material is generally termed as the energy of a unit cell divided by the number of atoms. what will be cohesive energy of an alloy in LAMMPS? I am running LAMMPS for $\ce{...
10
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1answer
95 views

How do I calculate the radial distribution function from the centre of mass of unit cell in GROMACS?

I am simulating a droplet of water with GROMACS. The droplet consists of about 200 TIP3P water molecules and is placed near the center of a large, mostly empty box (...
4
votes
1answer
49 views

Calculating Velocity autocorrelation function for Binary Diffusion Coefficient

I have been attempting for some time to evaluate the binary Diffusion coefficient of argon in a gas mixture with neon. From the literature, this property can be measured using the velocity ...
5
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1answer
39 views

Bulding host-guest polymer system for molecular dynamics

I'm thinking of running MD simulation of poling process (heating and cooling in external electric field) of host-guest polymer system: organic chromophore in polymer matrix (PMMA or polycarbonate). So,...
10
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1answer
143 views

What novel drugs are developed via CADD?

Virtual screening , protein ligand docking, MD simulation, FEP free energy calculations and the QM/MM approach have all been widely applied in optimization for drug discovery. Which drugs that have ...
12
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1answer
314 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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0answers
101 views

Calculate free energy for a canonical (NVT) ensemble [closed]

Note: Users wishing to answer this question may write a comment or a message in the chat indicating their desire for the question to be re-opened. I have an NVT ensemble of water molecules (liquid) ...
19
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5answers
2k views

What software is available to do molecular dynamics on Windows?

Is there a Windows-based molecular dynamics simulation software which is easy to use?
12
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1answer
87 views

Metropolis algorithm reduces energy in molecular simulation, but does not decrease euclidean distance

I am using an open source python package openmmtools to run a simple molecular simulation problem using the metropolis algorithm. I first load a default system of particles (alanine-dipeptide in ...
9
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2answers
436 views

Is the dynamics of a peptide molecule Markovian?

I was wondering if the underlying dynamics of a full atomistic trajectory of a peptide molecule are Markovian. Note added after the first two answers: I assumed that they were Markovian, as they are ...
6
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0answers
35 views

How to reproduce 2D small-angle X-ray scattering (SAXS) interferogram of water via ab-initio MD methods?

I am trying to reproduce the 2D SAXS interference pattern of bulk water via ab-initio MD methods as shown in the figure below: The main aim is to recreate figure (a) via averaging MD configurations ...
11
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1answer
78 views

Unable to recreate data for benzene from paper in GROMACS 2020.5

I have been trying to simulate benzene in OPLSS-AA forcefield as per this paper: https://pubs.acs.org/doi/10.1021/ct2002122. I have been at a loss, since I believe I have everything running as per the ...
7
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1answer
81 views

Using LAMMPS for a small system

I want to run a classical molecular dynamics simulation on silicane using LAMMPS. Since I don't have access to any HPC nor do I have a powerful desktop PC, I'm planning on making the system small. By ...
8
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1answer
141 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 $1 \,\mathrm{atm}$...
8
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1answer
114 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 ...
7
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1answer
161 views

Molecular Dynamics Simulations in VASP

I want to run molecular dynamics (MD) simulations with VASP for Mg2Si to investigate the simulation time vs ENCUT and KPOINTS, ...
8
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0answers
30 views

Lone pairs in CHARMM for molecular dynamics

I have a substrate that has a Br-C bond. In CHARRM the line below is included in the .str file: ...
3
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0answers
137 views

Error in GROMACS for adding ions to a solution

I am following Justin Lemkul's GROMACS simulation given on this website here for GROMACS. I believe I have followed the process to the T. I would like to mention that in the "Generate Topology&...
7
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2answers
93 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 ...
9
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2answers
102 views

Starting configuration for a molecular simulation

When doing a computer simulation, what’s the best way to prepare a starting configuration to avoid biasing your results? The book Computer Simulation of Liquids suggests putting the molecules on an ...
11
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3answers
396 views

Which ensemble to use for a molecular dynamics simulation?

Does it matter which ensemble you use for a molecular dynamics simulation? Shouldn't they in principle give the same results? Why, historically, was it hard (and desirable) to develop simulations in ...