[gmx-users] virial and external potential

Berk Hess gmx3 at hotmail.com
Thu Jul 22 15:22:10 CEST 2004

>From: Vincent Ballenegger <vcb25 at cam.ac.uk>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] virial and external potential
>Date: Thu, 22 Jul 2004 12:15:28 +0100
>When a system is confined by an external potential to a slit for example, 
>do we have to include the forces derived from the external potential to the 
>virial or not?

After discussing with Bert de Groot we have concluded that you
always have to include the forces from the external potential.
The only problem is how.
If all molecules are neutral the current Gromacs code is correct.
But if there are molecules with net charge in the system problems arise.
I think that these problems arise because the external field
is not self-consistent.

The error is probably small when the total system is neutral
and the are many ions present.
For other case I guess the only solution would be to use
a self-consistent field.

The correction I reported two days ago on the list is surely


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