[gmx-developers] question on PV term

Berk Hess hess at cbr.su.se
Tue Sep 29 09:43:06 CEST 2009


I would say there is not much point in this quantity.
One would not need it often, and if one would, you can simply
calculate it using the volume in the energy file.


Michael Shirts wrote:
> The PV term computed using pressure control is calculated as:
> pv = vol*enerd->term[F_PRES]/PRESFAC;
> i.e. the volume times the instantaneous pressure.  It's not clear to
> me there is a reason to compute this quantity. In the partition
> function, one uses P_ext V, where P is the external pressure that the
> system is maintained at, in the same way that when computing E/kT, you
> use the external temperature, not the instantaneous average of kinetic
> energies.
> It could be that there is a use for this quantity, but otherwise, I'd
> suggest changing it to
> pv = vol*trace(ir->ref_p)/(DIM*PRESFAC)
> or the tensor equivalent.
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