[gmx-users] Re: Enthalpy Confusion
Jeffery.Perkins at ufv.ca
Tue Jun 11 21:57:52 CEST 2013
>If you are computing enthaply in the NPT ensemble, P is constant, and
>is the applied pressure.
>The "pressure" quantity calculated from the KE and the virial is not
>the pressure. It is a quantity that when averaged over time is equal
>the pressure. Only the average is meaningful macroscopically.
Right, that's an easy one to miss but i don't think that's my problem here.
>If you are computing enthalpy in another ensemble (which is possible,
>though it may be harder to interpret) then you would use the average
>pressure from this quantity
I'm running in NPT and was calcaulating H from ave. P, ave. U and ave. V for
while i understand that this doesn't exactly equal average H it should be
close enough for me at this point, going back and redoing it with P set to
the reference value (which the average hits with small fluctuations)
the resultant H still doesn't line up properly for some example data:
"pV, g_energy" V, m^3 pV, J pV, kJ/mol
442.42 1.46E-26 1.46E-18 884.07
P = 1000 bar = 100,000,000 Pa
and i see that my pV is around 2x g_energies pV, no values are scaled for
the # of items in the box at this point, this is all for moles of the system
i think that's alright though
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