[Wien] Gauss-broadening"(G-b) in the DOS

[Peter Blaha]

I think it is rather clear that a larger "broadening" will make the 
"gap" smaller (and this of course arteficially).

Am 06.09.2012 08:51, schrieb Tiem Leong Yoon:
> We simulate a tantalate system using LDA+U. We use small k-points, 18,
> k-points, and SCF is done in less than 20 cycles. Then it is followed by
> LDA+U. After LDA+U, we do DOS  and bandstrtucture calculation separately.
>
> DOS calculation is straight forward in Wien2k. For our system, the space
> group is 13, and thus we refer to
> http://www.cryst.ehu.es/cryst/get_kvec.html
> <https://mail2.usm.my/owa/redir.aspx?C=6b51c784aa744c6aa0f9b75ad7f9c13e&URL=http%3a%2f%2fwww.cryst.ehu.es%2fcryst%2fget_kvec.html>
> to generate k-mesh, since we need to plot (Gamma, Z, Y, A, B, D, E)
> points and we believe that the default and available simple_cubic, bcc,
> hcp and fcc cannot generate the case.klist_band file we want.
>
> The problem now is the band-gap value from DOS and bandstrcuture
> calculation are the same if we do not do any "Gauss-broadening"(G-b) in
> the DOS. It means, if we stick to the default G-b of 0.003, band-gaps
> from DOS and Bandstrcuture calculation are basically the same. But if we
> change the G-b from 0.003 to, say 0.008, the band gap is observed to
> change to smaller value, >10% less than the value before.
>
> Can someone give the reasoning why there is such a difference occured?
> By the way, the reason why we adjust the value for G-b is because the
> graph will look more resemblance to experimental data plot rather than
> "spiky" features for smaller value of G-b
>
> and how to read the values for band-gap? do we read from DOS plot or
> bandstructure plot?
>
>
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671