On Mon, 26 Sep 2011 09:31:39 +0200
xiaojing gong <xnz...@gmail.com> wrote:
> Hi, many thanks for your answer.
>
> >> Any dynamical simulation has a lowest-energy structure... whether
> >> this
> means anything is another question.
>
> I am just wondering whether the structures you find with MD determined
> mainly by thermodynamics (i.e. the lowest energy structures) or by
> kinetics (i.e. the structures
> with the lowest activation barriers)?
The energy is NOT minimized in thermodynamics. The relevant quantity
that is minimized is the free energy. In NVT-simulations it's the
Helmholtz free energy
F = E - TS
where T is temperature and S the entropy. The minimum of F is obtained
in the struggle of minimum energy and maximal entropy. E is, however,
minimized when T=0.
In NpT you minimize the Gibbs free energy
G = E + pV -TS
where p is pressure and V is volume. Here to minimize E you would set
p=0=T.
--
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Mr. Jussi Lehtola, M. Sc. Doctoral Student
jussi.leht...@helsinki.fi Department of Physics
http://www.helsinki.fi/~jzlehtol University of Helsinki
Office phone: +358 9 191 50 632 Finland
--------------------------------------------------------
Jussi Lehtola, FM Tohtorikoulutettava
jussi.leht...@helsinki.fi Fysiikan laitos
http://www.helsinki.fi/~jzlehtol Helsingin Yliopisto
Työpuhelin: (0)9 191 50 632
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