[gmx-users] Meaningless pressure values: NVT and NVE ensembles

[Mark Abraham]

On Wed, Nov 5, 2014 at 1:17 PM, Francesco Mambretti <
francesco.mambretti at studenti.unimi.it> wrote:

>
> So you confirm me that pressure calculation in Gromacs is done through
> virial theorem and should provide meaningful results?
>

Yes, see manual section 3.4.3


> I start from a perfect fcc crystal and launch simulations of 20 ps...is it
> a
> too short simulation? density and temperature should be already optimized
> for argon solid state. However, I am trying to run simulations of 2000 ps.
> If the problem persists, I'll let you know.


I can't imagine anything under a nanosecond being useful, and for a system
that small, many nanoseconds is quite plausible. You should look at the
graphs of pressure over time. Since you're generating velocities, you
should be discarding the first fragment of your output.

Mark


> Thanks
>
> Francesco
>
>
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