Constant pressure

From: Kwee Hong (
Date: Thu Nov 25 2010 - 10:29:29 CST


I have my constant pressure control set as below during my equilibration

useGroupPressure yes
useFlexibleCell no
useConstantArea no

langevinPiston on
langevinPistonTarget 1.01325
langevinPistonPeriod 100.
langevinPistonDecay 50.
langevinPistonTemp $temperature

yet when I analyze my log file with NAMD plot, my pressure was found to
fluctuate between -300 bar and 300 bar. Is this normal?
When I read through the mailing list, someone says that this is caused by
small size of the system. And another comments fluctuation of plus minus 50
bar is normal.

please advice and thannks in advance.


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