AMBER Archive (2004)

Subject: Re: AMBER: Constant Pressure Problem of MD

From: David A. Case (
Date: Mon Jun 07 2004 - 21:12:41 CDT

On Mon, Jun 07, 2004, Nan Lin wrote:
> I am running MD for a complex of protein + ligand with WAT under constant
> pressure. I can get a fairly equilibrated system after 500ps run. But the
> pressure value is not stable at all. It constantly changes in a range from
> -1000 to +1000, also the mean is around 0-1. I read some previous posts
> saying the pressure is not constant, but changes should only be in a range
> of a couple of hundreds. Anybody know what's the possible problem in my
> system?

It sounds like you are fine. The magnitude of pressure fluctutaions depends
on the taup value used, and on the size of the system. See

for more info. The difference between a "couple of hundreds" and 1000 is not
all that great.


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