Gibb's Free energy and Chemical Potential

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sharma · #1 Post by **sharma** » Mon Sep 05, 2011 5:16 am

I want to calculate the surface free energy find the stable surface termination. As I read we need to know Gibb's free energy and chemical Potential.

My question is "How can we calculate the Gibb's free energy and chemical potential from VASP?"

Is Free Energy (F) and Gibb's free energy Same in VASP? F = U-TS.

I want to calculate the stable surface termination in Pt3Ni(001), so i need the values for Pt and Ni.

I appreciate your valuable suggestions.

Thank you.

Sharma

alex · #2 Post by **alex** » Mon Sep 05, 2011 12:33 pm

Hi sharma,

it does not work in an automatic way. You have to do it by hand:

a) calc. the minimum energy structure
b) make a frequency calculation
c) calc. from the modes the zero-point energy and the contributions to H and S

Cheers,

alex

PS: One of my papers contains an outline: JPC B 108 (2004) 14652-62

vistawanted · #3 Post by **vistawanted** » Wed Sep 14, 2011 6:10 am

In first principle area, we normally use G(T) = H_conf + H_vib -T*S_conf - T*S_vib, where H_vib and S_vib are calculated through phonon calculation (by Frozen-phonon or DFPT method) and quansi-harmonic approxmation (QHA). If the pressure was 0, enthalpy equals to internal energy. Then we can change the formular to G(T) = E_tot + F_vib(T).