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

Berk Hess gmx3 at hotmail.com
Wed Jul 5 09:11:49 CEST 2006

>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 
>nstcomm (earlier with small nstcomm I did observed anomalous behaviour 
>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?

Are you talking about the center of mass of the total system
or the centers of mass of the surface and water?

The center of mass of the total system is a free degree of freedom.
Since no forces are working on it, its momentum should not change.
But do to integration errors it could. To avoid this annoying, though
unharmful, behavior one should use comm_mode=linear, ntscomm=1.

You can not remove the separate com motion of the surface and
the water as this would influence the process you want to study.


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