RE: Pressure is not constant in NPT ensemble

From: Parisa Akhski (
Date: Sun Aug 01 2010 - 13:31:11 CDT


I am just wondering how much deviation form the target pressure is allowed in NPT ensemble by NAMD when using "LANGEVIN PISTON PRESSURE"?

According to the

it seems that in order to check the reliability of the pressure, we need to run a constant volume cutoff simulation in a cell that is larger than the molecular system by at least the cutoff distance; so, the pressure for this isolated system should average to zero over time. I set the pressure on 1bar and in the output file it starts form a big negative value and goes up but fluctuates between -50 and 50 bar (does not get zero finally). Is this OK or does anyone have any suggestion?



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