[gmx-users] problem with the pressure

Mark Abraham Mark.Abraham at anu.edu.au
Fri Nov 25 14:18:46 CET 2005

Rongliang Wu wrote:
> Hello gmx-users,

> i've made a system of 4 4 4 water box using -ci and -nmol,  after
several nanoseconds of MD the system still posseses a pressure of about
50 bar(reference pressure is 1 bar), and the pressure decresses rather
slowly, is there any way to make the system equalize more faster? are
the densities of the system in gromacs comparable to the real ones? will
the system come to equalibrium aroud the reference pressure anyway with
long time run if the density of the system is somewhat large or small?

If you just want a box of water, why aren't you using "genbox -cs
xxx.gro -box i j k" or similar?

It sounds like whatever you've produced has some serious physical
problem, such as an inappropriate density. You should be able to measure
that using g_energy. Are you using T-coupling? Are you looking at the
average pressure and not an instantaneous one?

Is the time constant on your P-coupling small enough?


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