Gibbs Free Energy and VASP

[markmick]

I've successfully performed binding energy calculations with VASP, but I'm stumped with Gibbs free energy. Based on an article I'm studying, Gibbs Energy for an adsorbed hydrogen is calculated by:

ΔGH = ΔEH + ΔEZPE - TΔS

Some of these variables I understand, others I don't:

* T is temperature in Kelvin (Setting this in INCAR I believe)
* ΔS is entropy, which I believe is pulled from OUTCAR
* ΔEH is the binding enegy, and I know how to do this one
* ΔEZPE (Zero-point-energy). This one has me stumped.

ΔEZPE = ΔEnH - ΔE(n-1)H - 1/2 EH2

ΔEZPE has something to do with meV and THz values pulled from OUTCAR. My INCAR is set with:

NELMIN = 4
ISMEAR = 0
IBRION = 7
ISIF = 0
LEPSILON = .TRUE.
NSW = 1
NWRITE = 3

and this produces an OUTCAR with final values like:

63 f = 0.665149 THz 4.179253 2PiTHz 22.186976 cm-1 2.750835 meV

How to translate this OUTCAR data into the values for ΔEZPE elude me. I assume just use the meV value? Thanks for any assistance. I'm accustomed to Gibbs from Thermodynamic calculations, but using VASP for this is a new frontier.

Sincerely,
Mark

[admin]

Entropy in OUTCAR is entropy of electrons.
To calculate entropy of atoms you need to perform the frequency analysis.
Details how to evaluate S and ZPE you can find in the basic literature,
e.g. F. Jensen, Introduction to Computational Chemistry, Wiley