[gmx-users] COM motion removal

[Berk Hess]

>From: Janne Hirvi <janne.hirvi at joensuu.fi>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] COM motion removal Date: Tue,  4 Jul 2006 16:45:09 
>+0300
>
>Hello gmx-users!
>
>I have one question about the center of mass motion removal. If I use for
>example 'nstcomm = 100' do I remove the net momemtum by rescaling the
>velocities (or by some other method?) after every 100 time steps and the 
>center
>of mass can still move during other time steps but I reset the development 
>of
>net momentum for a while?

You can't rescale.
You just step the COM velocity to zero every 100 steps.
The other the COM can develop moment.
So you do not reset the development, you reset the momentum.
Otherwise the COM would always have momentum.

The question is if we need the option nstcomm.
We should time if it has any significant impact on the performance,
if not we should always use nstcomm=1.

Anyhow, set it to 1 you will not notice the difference in performance.

Berk.