[gmx-users] Re: pull forces

Thomas Schlesier schlesi at uni-mainz.de
Tue Mar 15 18:25:03 CET 2011

> Message: 5
> Date: Tue, 15 Mar 2011 07:17:28 -0700 (PDT)
> From: Michael Brunsteiner<mbx0009 at yahoo.com>
> Subject: [gmx-users] pull forces
> To: gmx users<gmx-users at gromacs.org>
> Message-ID:<613152.30411.qm at web120517.mail.ne1.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
> Dear all,
> does anybody know what the forces that are saved
> in the f*xvg files from the pull-code actually are? are these:
> 1) the (sum of the) forces due to the normal non-bonded interactions
>      in the system acting on the ref and the the full groups.
> 2) only the forces from the harmonic restraint.
> 3) the sum of both?

if you mean the pullf.xvg it's 2. only the force from the harmonic 
restraint (if you're using 'pull=umbrella')

> i just did a test writing out the forces from the trajectory
> file, and looking at the relevant forces (the ones in the z-dimension
> in my case, as i use pulldim N N Y and constrain the groups to stay
> put in the x and y dimensions) it seems as if the forces on the
> pull group are oscillating as expected, but the forces on the
> reference group are close to, but not exactly(!) zero.
> i am not sure how to interpret this ...
> cheers
> Michael

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