[gmx-users] inserting a new potential

David L. Bostick dbostick at physics.unc.edu
Fri Jul 25 15:26:01 CEST 2003

There is a separate directive for Electric fields: "E_x; E_y; E_z".  See
the manual for all mdp options. The options, "acc_grps" and "accelerate"
should do just what you want. All atoms in the groups listed under
acc_groups in the mdp file will experience a constant acceleration.

So if you want to impart a constant acceleration to all atoms in the system
due to "gravity" in the z-dimension, just recall from
high-school physics that g= 9.8 m/s^2 and convert it to nm/ps^2 units
for the mdp file. Set

acc_grps = System
accelerate = 0.0 0.0 -g

Since I don't know what you're trying to do, I can't offer many specific
ideas about pbc or anything else. Are you trying to simulate falling

Good luck!

> Alan Wilter Sousa da Silva wrote:
> > Thanks David Bostick,
> >
> > I'll take a look abou acc-grps. Related to Forced Simulations?
> >
> I always considered these directives to be useful for
> simulation of an electric field. you have to define
> a group for each type of charge of course.
> If gravity should be modeled pbc has to be turned
> off in that direction, hasn't it?
> regards
> --
> Christoph Freudenberger
> Abt. Organische Chemie I AK Siehl - Uni Ulm -Tel: ++49-731-502-2785
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