COM position

From: Mauricio Carrillo Tripp (
Date: Mon Jul 05 2004 - 14:47:51 CDT

Hi all, I'm not sure this went through last time (I haven't got any
replies) , so I'm sending it again with more coments...

Is there a way to keep the system's center of mass position fixed at a
certain point (e.g. origin) ?
is there a command in NAMD to accomplish this or do I have to write a
script? How do I do it?

Reading the manual I found in section 6.7.3 and 6.7.6 (Options for
restraints and Examples, Fixed restraints page 80) that I can do something

urestrain {
  posi group {(*,*,*)} kf=20 ref=(0,0,0)

I'm not sure about the *'s though, should I use {all} instead?
Would this work?

Afterall, all I want to do is to keep the COM from moving in the Z
direction... it should be something quite simple, but I'm not sure
how to do it.

Thanks for any help

Mauricio Carrillo Tripp
Chemistry Department
Wabash College

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