phase equilibria using NAMD

From: nasrat kamal (
Date: Wed Jul 21 2004 - 07:33:45 CDT

Hello, I am using NAMD to perform simple MD simulations in NPT ensemble to calculate equation of state, phase equilibria and other thermodynamic properties of isobutane, isobutene and N-methyl-2-pyrrolidon. I have estimated phase equilibria for NMP but the critical point is coming out to be 100 K lower than the experimentally obserbed value. This can happen if the expression for tail correction (due to truncation of potential) is not included while calculating pressure and energy. Does anyone knows if NAMD also incorporates tail correction in the simulations? If not, then how can we include that? I have already performed simulations and I would also like to know if I can incorporate the corrections directly to the results. Also, in NPT ensemble simulations, the pressure is not at all constant, but shows fluctuations upto +-1000 bars. Does this means that there is something wrong in the simulations ?? Looking forward for your help, Many thanks, Nasrat.

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