[gmx-users] RE: heat capacity etc. (Thomas Koller)

David van der Spoel spoel at xray.bmc.uu.se
Sat Mar 12 09:43:21 CET 2011

On 2011-03-12 07.52, Thomas Koller wrote:
> Thanks,
> the equation for the heat capacity is:
> c(P) = delta(H(average))/delta(T(average))
> So do it have to take the fluctuations (which are listed with g_energy) of U(tot) and pV as well as of T to calculate c(P)? The problem is the delta.
> The same is with the thermal compressibility:
> a(P) = 1/V(average) * delta(V(average))/delta(T(average))
> Another question: Why should I take U(tot) and not only the potential for c(P)? The same is for the heat of vaporization, here also with U(tot)?
> Regards,
> Thomas
You need to compute the enthalpy = Etot + pV. The fluctuations in Etot 
and pV are correlated and compensate each other to some extent, and 
hence you need to sum the two first and compute the fluctuations afterward.

David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
spoel at xray.bmc.uu.se    http://folding.bmc.uu.se

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