Re: obtaining the system force

From: Giacomo Fiorin (
Date: Tue Dec 24 2013 - 10:51:10 CST

Hello Neelanjana, you could define three collective variables that are the
Cartesian components of the center of mass of the subsystem you want, and
output the system force on it.

I trust you know that if you do this for the entire system, the total
system force will be zero except for small errors due to cutoffs and a
finite grid size for PME.


On Tue, Dec 24, 2013 at 1:26 AM, Neelanjana Sengupta <>wrote:

> Dear experts,
> Does NAMD allow one to print out the total *force* acting upon the system
> (or a sub part of it---say the protein molecule in a protein-solvent
> simulation) at every timestep of an unbiased simulation?
> Some suggestions would be highly appreciated.
> Thanks,
> Neelanjana

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