[gmx-users] Cannot obtain the expected pressure using the Parrinello-Rahman coupling in a gas-liquid system

GuoGuangjun guogj at hotmail.com
Sat Feb 28 13:14:59 CET 2009

Hi, All,

I am simulating an interface system composed of methane gas and liquid water in the NPT ensemble. The temperature is well controlled by using either the Berendsen or the Nose-Hoover T-couplings. As for pressure, the Berendsen P-coupling also works well. However, the Parrinello-Rahman P-coupling always produces a higher pressure than the expected. For example, I set ref_p=300 bar in the mdp file but obtain an average pressure as ~330 bar (over 0.5 ns). I test the tau_p in the range 0.1 ~ 10 ps, the case does not change. When I test the single-phase system, i.e., pure water, the Parrinello-Rahman P-coupling can indeed produce the expected pressure with the deviation less than 2 bar. What is the matter in the two-phase system?


Thanks a lot.


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