[Wien] Fermi level of band plot

[Peter Blaha]

For a metal, certainly only EF from the scf calculation is ok.

For an insulator/semiconductor, we give EF at the valence band maximum. 
This could be at Gamma, or at some other k-point in the BZ.
If the VBM is at Gamma and you use a shifted k-mesh, you do not have 
Gamma in your scf-mesh and thus the EF from the scf calculation will be 
too low, while EF from the bandstructure (when it includes Gamma) is the 
correct one.

On the other hand, if the VBM is at some other k-point (eg. L), but you 
plot the bands from Gamma-X only, this EF is NOT correct either, but 
maybe the scf-EF is better (correct).

So in essence: there is no "simple" answer 1) or 2) is correct, but you 
must "think".

Regards

On 5/29/19 4:23 AM, 徐远骥 wrote:
> Dear WIEN2k users：
> 
>      When I plot band structures in some cases， the value of the Fermi 
> level ':FER' are not the same in case.scf and case.scf2(up). In some 
> cases, the difference can be get large to 0.1 eV.
> Which one should I need to use ?
> 
>      In my understanding, the ':FER' in case.scf should be more precise, 
> because we using all the k-points to calculate the Fermi 
> energy. However, in band plot(-band) mode, we only using the k
> point along high-symmetry path. In fact, I don't know how to calculate 
> Fermi level in case.scf2(up) in band plot mode.
> 
>      What makes me confusing is: in one semiconductor type material 
> calculation, using scf2 Fermi energy can give a nice gap. But the Fermi 
> energy in case.scf will causing a little touch of Fermi level to the top 
> of valence band.
> 
> 
> Best regards!
> 
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:  http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
> 

-- 

                                       P.Blaha
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
--------------------------------------------------------------------------