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I've been calculating the adsorption/dissociation and association/desorption (enthapy) energies of different gases on a metal surface using periodic calculations with PAW potentials.
I now want to calculate the Gibbs' free energy of the reactions, by taking into account the entropic contributions of the gases.
i.e. dG = dH -TdS

How do I calculate entropy using periodic calculations?

I'm a new user to Vasp, so any help would be welcome.
Thanks Natasha

Entropy will have contributions from translation, rotational, vibrational, electronic for each atom. Translation part is negligible in solid (0.5kT per DOF), vibrational part in fact all contributions can be calculated from standard thermochemistry calculation once vibrational frequencies are known, then degeneracy of the electronic state of the atom.

Codes for doing standard thermochemistry calculations are available in the internet. If you need one, send me email, I have some.
<span class='smallblacktext'>[ Edited Sun Sep 17 2006, 09:48AM ]</span>