[WIEN]Why Fermi Energy is positive

[Jiang Jun]

Dear Blaha:
    I believe it is so simple a question to you,but it is a litle hard for me 
to understand the positve Fermi energy.We all know that the energy of an atom 
or a molecule is a negative quantity and A positiv value means that the 
system is unstable.

    To my opinion,there must a different rule in choosing the zero point of 
potential in LAPW(or APW) from popular molecule-calculation programs 
e.g.Gaussian or ADF,in other words,How to determine the zero point of 
potential in LAPW?Is it in in Interstitial zone?

    By the way,If I want to find the energy of Exc(Exchange-Correlation 
energy) from case.output* or case.scf, where is it?Whether just the total 
energy is outputed in case.scf?

    Thank you greatly!
Best regard!
                                               Sincerely Jun
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