[gmx-users] Re: Pressure control in GROMACS 4.0.7

Vitaly Chaban vvchaban at gmail.com
Sat Jul 10 12:40:03 CEST 2010

Dear Professor van der Spoel:

Don't you have an idea why the average value of pressure appears to be
(always?) slightly larger and (never?) smaller than requested one? I
did not collect the statistics systematically but I often mentioned
this curious fact.


> fluctuations are proportional to 1/sqrt(natoms). The numbers Zhongjin
> mentions are extreme, for a 216 water box *in equilibrium* you would get
> 1 +/- 500-600 bar. I suspect your sytem may be out of equilibrium or
> very small. Whether the average is 1 or 5 does not make a difference if
> the fluctuation are two orders of magnitude larger.

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