# [gmx-users] Gibbs free energy

mohammad agha mra_bu at yahoo.com
Tue Dec 25 05:49:32 CET 2012

```Dear Steven,

Many thanks from your help. In the manual at the section g_energy has been written that the gromacs calculate the delta G as is follows:
"Delta G = G(N,p,T) - G idgas(N,p,T) = kT ln < eˆ(Upot/kT) >"
But I don't understand why Upot? to calculate of delta S, I know that "delta S = (internal energy + P*delta V- delta G)/T" but here has been written: Delta S(N,p,T) = S(N,p,T) - S idgas(N,p,T) = (<Upot> + pV - Delta G)/T.

Best Regards
Sara

----- Original Message -----
From: Steven Neumann <s.neumann08 at gmail.com>
To: mohammad agha <mra_bu at yahoo.com>; Discussion list for GROMACS users <gmx-users at gromacs.org>
Cc:
Sent: Tuesday, December 25, 2012 2:26 AM
Subject: Re: [gmx-users] Gibbs free energy

Obviosuly not. Total energy in MD = total potential energy + total
kinetic energy. Read basis of MD. There are specific methods to get
free energy which you should aslo read about.

Steven

On Mon, Dec 24, 2012 at 6:21 PM, mohammad agha <mra_bu at yahoo.com> wrote:
> Dear GROMACS Users,
>
> I work with NPT ensemble. Is the total energy equal to Gibbs free energy?
>
> Thanks in advance.
>
> Sara
>
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```