[gmx-users] Re: Re: COM motion removal

Janne Hirvi janne.hirvi at joensuu.fi
Tue Jul 4 19:15:57 CEST 2006

> >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.

In my case I need to see COM motion when my water droplet (starting from
spherical droplet) is spreading on a surface, but I used option 'comm_mode =
none' and now I think that I should have used 'comm_mode = linear' with large
nstcomm (earlier with small nstcomm I did observed anomalous behaviour without
clear spreading) so that I actually see that droplet spreads but I wont see
large lateral motion of COM? Do you have a comment on that?

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



Janne Hirvi, MSc(Physical Chemistry), Researcher
University of Joensuu, Department of Chemistry, P.O.Box 111 80101 Joensuu, FI
Tel: +358 13 2514544 & +358 50 3474223
E-mail: Janne.Hirvi at joensuu.fi & hirvi at cc.joensuu.fi

More information about the gromacs.org_gmx-users mailing list