[gmx-users] Re: Enthalpy Confusion
David van der Spoel
spoel at xray.bmc.uu.se
Wed Jun 12 19:17:44 CEST 2013
On 2013-06-11 23:31, Jeffery Perkins wrote:
>>> or should i be doing < U+<V>*ref_p > = <H>?
>> More specifically, <U> + <V>*ref_p = H
>> <H> isn't really meaningful thing. I mean, you can define something
>> such that <H*> = H, but that's not really thermodynamics.
> sorry I always have issues deciding how to talk about this stuff, so thanks
> for putting up with my terrible notation =)
>>> example system gives <H> = -1168 kJ/mol and i find <H> = -725 kJ/mol
>> Interesting. What material at what phase conditions? For liquids,
>> the PV contribution should be very small.
> I hadn't really thought about that... but the system is a monatomic
> Lennard-Jones particle (uncharged sigma = 0.35 nm epsilon = 2 kJ/mol mass =
> 40 amu) which should be a liquid at the conditions I was looking at, P=1000
> bar, T = 300 K using phase diagram in: Equation of state for the
> Lennard-Jones fluid, J. J. Nicolas et al., MOLECULAR PHYSICS, 1979, VOL. 37,
> No. 5, 1429-1454
> the <U> is -1600 and the p<V> is 880 when manually done, around 400 from
Here's the code:
/* This is pV (in kJ/mol). The pressure is the reference
not the instantaneous pressure */
pv = vol*md->ref_p/PRESFAC;
add_ebin(md->ebin, md->ipv, 1, &pv, bSum);
enthalpy = pv + enerd->term[F_ETOT];
What is your volume?
What is Etot?
PRESFAC ~ 16.6
> View this message in context: http://gromacs.5086.x6.nabble.com/Enthalpy-Confusion-tp5009053p5009068.html
> Sent from the GROMACS Users Forum mailing list archive at Nabble.com.
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
More information about the gromacs.org_gmx-users