Alpha Z

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physicsdude · #1 Post by **physicsdude** » Fri Sep 19, 2008 10:51 pm

I'm having some strange output from VASP in the VASP OUTCAR, specifically the alpha Z term in the free energy.

I have a supercell with an interstitial atom, say 8 lattice atoms and an interstitial atom and I compare the alpha z term. By looking in OUTCAR, I compare the alpha z for this case to the case where I have 8 lattice atoms and I multiply the the alpha z by 9/8. The two numbers I get don't agree.

Does anyone have any idea what is going on here? As I understand it, alpha z is just a straightforward integration of the atomic psuedopotential over the entire unit cell; it should be linear in the number of atoms (of a given species). Given that the supercells are the same size, are there any conditions that would change the alpha z value for a supercell with a given atomic composition?

Thanks!

#2 Post by **admin** » Thu Sep 25, 2008 9:42 am

alpha Z is the diverging (G=0) contribution of the electrostatic interaction with the compensating electron gas.