Pressure fluctuations

From: Cyril Falvo (
Date: Thu Apr 05 2007 - 14:30:13 CDT


I don't have any experience in molecular dynamics. I am just trying to
equilibrate a solvent box (chloroform) in a NPT simulation.
I am using Langevin piston with the typical parameters
(*LangevinPistonTarget = 1.01325 bar, **LangevinPistonPeriod = 200 fs,
**LangevinPistonDecay = 100 fs*).
During my simulation the temperature fluctuations are reasonable but the
pressure fluctuations are very very large. I found in namd mailing list
some messages
about pressure fluctuations, In
this last message it is suggested that these fluctuations are normal
I understand that both T and P have to fluctuate. However, when the
fluctuations are much higher than the targeted value, I don't understand
the physical meaning of this.
Does these fluctuations are normal ? Do you think I made a mistake in my
simulation ?
Thanks for your help.



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