[Wien] Suspicious Fermi energy values

[Peter Blaha]

The Fermi energy (or some eigenvalues) do not have any meaning as 
absolute values. We have an infinite solid, no vacuum and the constant 
in the coulomb potential determination is set "arbitrarely" to its 
average in the interstitial region.

Thus your energy-zero is different for the 2 systems and you cannot 
compare these numbers.

Possible solution: Try to find a common energy scale, eg. by comparing a 
Zn-core level and relate all energies to these numbers (does not work if 
the ionicity is different ....)

Do slab calculations with a vacuum and relate the energy to the 
potential in the middle of the vacuum.

Am 19.02.2013 05:16, schrieb dileep at jncasr.ac.in:
> Dear users,
>
> I am studying the band gap and the valence band offsets of ZnO and ZnS using mBJ exchange correlation potential in WIEN2k12.1 . It is well established using theory and experiment (also it is intuitive)that the valence band offset of ZnS is higher in energy than that of ZnO by ~ 1 eV (DOI: 10.1103/PhysRevLett.97.146403). But I am getting the valence band offsets
>
> ZnO - 0.39378 Ry
> ZnS - 0.24021 Ry
>
> What could have gone wrong?
> I am using a single unit cell in both cases with Wurtzite structrures
> I am using 76 irreducible k points in both cases (put 1000 as input in k-gen).
> RKmax in both cases are 7.00
> The c-parameter in mBJ potential were given according to the 'P-semiconductor' scheme in 10.1103/PhysRevB.85.155109
>
> -Regards
>   Dileep Krishnan
>   c/o Dr. Ranjan Datta
>   ICMS, JNCASR,
>   Jakkur
>   Bangalore, India - 560064
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>

-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671