[gmx-users] isothermal compressibility- OPLSAA at high pressure

[Juliette N.]

Hello Dear all,

I have a few short questions about pressure coupling settings, namely
isothermal compressibility. I hope you can guide me.

A) By default gmx is taking the value for water but I was wondering if this
has to be modified for other systems.

B) This quantity varies with T and P. so if I am to perform different NPT
runs ( different P runs), Do I have to put in corresponding isothermal
compress. for each pressure or it doesn't really matter? (because it is of
the order of 10^-5). Now I am using an average value for the pressure range
I am working with, which is about 3 times higher than that of water.

C) Once NPT run is done, g_energy reports another isothermal
compressibility!. My question is if it takes this parameter as an input what
is the value g_energy is reporting? (although it seems what gmx reports is
not really accurate according to some of the posts in the archive).

last Q) and my last question is about validity of OPLS-AA forcefiled at high
pressures. Could you please explain if employing oplsaa is restricted to a
certain pressure (or temperature) ? Does the accuracy of results change from
say 10 to 500 bar? I did not find any answer to this question in the list
archive.

-- 
Thanks,
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