Langevin Dynamics in Gromacs

User discussions
1

GROMACS version:2022.1
GROMACS modification: Yes/No
Here post your question
I am dealing with molecular dynamic simulations of ions in vacuum using Gromacs .
Currently I want to apply Langevin force to my system that is of just KCl crystal so that it gets random forces from random directions but in a way that it applies random force to the whole crystal i.e. to a group of atoms rather than just each atoms of K and Cl.
Is it possible in Gromacs to apply langevin dynamics and hence random force to the whole crystal at once rather than to each atom as it usually does and I will be highly obliged if someone can kindly tell me how can one achieve this if possible. My aim is to just move the whole crystal around the box for the time being.
Thank you very much for taking the time to read the query and hoping to get a solution or advice regarding the problem

2

That is not possible.

Why do you want to do that?

3

Thanks a lot for your answer.
I want to study the collisions of KCl crystals among themselves hence initially I wanted to start with one crystal first to check whether I can apply random force to the COM of a group of atoms so that the crystal can traverse around the box randomly. Then use the same parameters and introduce more KCl crystals in the system and study the collisions of these KCl crystals and the ways they are interacting with other crystals through simulation using GROMACS.

4

You have more control by setting up the initial state directly. With gmx editconf you can translate and rotate individual crystals. You then need to add the same velocity to the whole crystal. There no GROMACS tool for this, so you would need to write a script. Then you can paste the crystals together in one gro file.

5

Thank you very much for your reply. I will definitely work on that.
Thanks a lot