[gmx-users] Re: pressure of the liquid in NPT and NVT

Vitaly Chaban vvchaban at gmail.com
Wed Nov 3 00:15:44 CET 2010

> Unless the box was equilibrated at NPT at the start of the NPT run, or the
> run was very long, the average value over the whole run is not all that
> likely to be one from the equilibrium range. Take the last frame.

The system is pretty equilibrated. Just look at the energy drift - it
is negligible.
> We had a thread about this last week, and numerous more in the past. These
> observations are strongly dependent on the length of time over which you
> observe the average pressure, and the size of the system. Note that your
> fluctuations dwarf your average... See
> http://www.gromacs.org/Documentation/Terminology/Pressure_Coupling

Yes, we had such discussions, but the main question is if this is
possible to get the same average pressure using NVT as I had in the
NPT. If no, I am just curious about the physical background of this

I believe, the average value should make sense. In the present case
the simulation time is 1 ns and the number of waters is 1728. I used
shorter intervals within this run and the pressure values (average, of
course) were always between -10 and -20 bar.


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