**From:** Jérôme Hénin (*jhenin_at_ifr88.cnrs-mrs.fr*)

**Date:** Thu Oct 28 2010 - 11:58:00 CDT

**Next message:**mjyang: "questions about ABF simulations"**Previous message:**Phil Miller: "Re: [ppl] error compiling charm-6.2.2 for bluegenep-xlc"**In reply to:**divya nayar: "Enthalpy calculation"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

Hi Divya,

You cannot reasonably compute the enthalpy, since the value of U given

by the force field has no absolute meaning because it has an arbitrary

energy reference : only differences between two states of the same

system are meaningful.

However, it might make sense to compute an enthalpy difference between

well-chosen systems. Although in that case, one is more typically

interested in the NPT ensemble, and the change if PV is often

negligible, so what is significant in the end is the change in average

potential energy. The key word here is 'average'.

Cheers,

Jerome

On 28 October 2010 17:12, divya nayar <divya.alchemist_at_gmail.com> wrote:

*> Hi,
*

*> i am simulating (NVT) system of peptide+ water. I want to compute enthalpy
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*> of this system. Will it be correct to do
*

*> H= U+PV and use the values of potential energy (is it correct to assume it
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*> to be internal energy?), pressure and volume form the simulation data to
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*> calculate H?
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*> Please help.
*

*>
*

*> Thanks,
*

*> Divya
*

**Next message:**mjyang: "questions about ABF simulations"**Previous message:**Phil Miller: "Re: [ppl] error compiling charm-6.2.2 for bluegenep-xlc"**In reply to:**divya nayar: "Enthalpy calculation"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

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