RE: Pressure is not constant in NPT ensemble

From: Nikolaos Glykos (glykos_at_mbg.duth.gr)
Date: Sun Aug 01 2010 - 15:37:17 CDT

Search the archives. It has been discussed over-and-over again. You
could even predict the magnitude of the fluctuations expected for your
system.

----- Μήνυμα από Parisa.Akhshi_at_chem.queensu.ca ---------
     Ημερομηνία: Sun, 1 Aug 2010 14:31:11 -0400
            Από: Parisa Akhski <Parisa.Akhshi_at_chem.queensu.ca>
           Θέμα: RE: namd-l: Pressure is not constant in NPT ensemble
           Προς: Ajasja Ljubetic <ajasja.ljubetic_at_gmail.com>
    Κοινοποίηση: namd-l_at_ks.uiuc.edu

>
>
> Hi,
>
> 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
>
> http://www.ks.uiuc.edu/Research/namd/2.6/ug/node32.html
>
> 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?
>
> Thanks,
>
> Parisa
>

----- End message from Parisa.Akhshi_at_chem.queensu.ca -----

This archive was generated by hypermail 2.1.6 : Wed Feb 29 2012 - 15:55:59 CST