[gmx-users] System drift with velocity verlet integrator

[Kristoffer Enøe Johansson]

Dear GMX users,

I am tryng to simulate a solid molecular crystal but the system builds up translational movement when I use the md-vv integrator with or without pressure coupling. With the leapfrog integrator this never happens. The md-vv integrator is interesting for me for comparison with another software.

Without symmetry constraints translation is indeed possible with close to zero friction for a crystallografic (periodic) cell but the center of mass removal should prevent this from happening.

Setting nstcomm=1 and comm-grps to a central part of the system had no effect at all. In using gromacs 4.6.7.

Any comments or ideas are welcome since I am stuck with this. I can provide any input/output files on request.

Kind Regards
Kristoffer Johansson
Computational Materials Science
Department of Pharmacy
University of Copenhagen