[Pw_forum] Determining Bandgap with DOS

[Giuseppe Mattioli]

Dear Izaak
Wurtzite ZnO is a very (VERY) nasty semiconductor... I find a PBE band gap of 0.8 eV, in agreement 
with previous investigations. Hybrid functionals, as HSE with alpha=0.25, do not heal the whole of 
it; you find something around 2.2 eV (If you are interested, I can cite several papers). This is due 
to the very narrow Zn 3d band which is very strongly affected by delocalisation (aka self-
interaction) errors. The conduction band minimum (CBM) appears as a tiny feature (the 0.5 eV one, I 
suppose) in your DOS because the CB is sharply peaked around Gamma, so that even if your calculation 
is well converged wrt energy, forces, stress, ..., you do not achieve a good sampling around the 
CBM. How can you cure it? It depends on your final purpose, which I suppose is not the band structure 
of a 4-atoms cell... You mat write directly to me if you are going to look for further advice.
HTH

Giuseppe

On Thursday 17 May 2012 23:43:45 Izaak Williamson wrote:
> Hello all,
> 
> I am trying to calculate the electronic bandgap for wurtzite ZnO using
> the attached plot of DoS (E), where the Fermi level is represented by a
> vertical
> 
> dashed-line and EV represents the valence band maximum.
> 
> My question is, should I use EC1 or EC2 as my conduction band minimum?
> If I use EC1, the bandgap is ~0.5eV but if I consider those states at
> that point negligible and use EC2 then the bandgap is ~1.5eV. (NOTE:
> 
> the experimental bandgap is 3.36eV.)
> 
> Thanks for the help.

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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