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