[gmx-users] Re: How do gromacs remove center of mass of a group?

zcwang zcwang at mdl.ipc.pku.edu.cn
Mon Oct 20 16:15:15 CEST 2008

Yeah, maybe my discription is a little bit complicated.

Well, what I understand of the center of mass removal, e.g. linear
removal, is that, the center of mass is not actually contrained or
restrained, it's just that all velocities in the system are simply
substracted by the velocities of the COM of the group every nstcomm

So in fact, the COM of the group is still moving in absolute space,

For example, if I add a force to a protein in a water enviroment while I
set the COM of the protein to be removed linearly, then the protein will
not actually stay stationarily in terms of COM as to the water
environment, but it will be dragged in the water environment, feeling
the friction of water mainly in the direction against the pulling

I wonder if my understanding of the COM removal algorithm is right.

在 2008-10-20一的 15:52 +0200,gmx-users-request at gromacs.org写道:
> zcwang wrote:
> > Hi all
> > I would like to know how gromacs remove center of mass motion?
> The COM velocity is the rate of change of the position of the COM,
> i.e. 
> the mass-weighted average velocity of the particles. If you subtract 
> that from each particle velocity, the COM velocity becomes zero. 
> Likewise for angular motion, if applicable.
> > I thought it still allowed center of mass motion, but just did a
> > transformation of the coordinates at a certain frequency.
> I've never heard of GROMACS doing anything like that for this purpose.
> > It's just like looking at the system in a noninertial system
> attached to
> > the COM of the group.
> > Is that right?
> I don't know what you mean.
> Mark

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