GuoGuangjun wrote:
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?
When I've used the Parrinello-Rahman barostat for membrane systems, it works
just fine. Perhaps 500 ps is too short of a timeframe to arrive at the average.
Heterogeneous systems often take longer to equilibrate.
-Justin
Thanks a lot.
Guang-Jun
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--
========================================
Justin A. Lemkul
Graduate Research Assistant
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
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