[Wien] band gap problem

[Stefaan Cottenier]

> I'm doing calculations on Mg2Sn, a semiconductor with a small indirect
band
> gap of about 0.3 eV. The calculations converge well, but the band gap is
> underestimated significantly and valence and conduction band already
overlap
> slightly and I get a semimetal structure (attached).
> I’m not sure how this influences the results (most important the
dispersion
> relation of the conduction band). How bad is it and is there a chance to
> correct this somehow? Did I do something stupid?

Most likely you observe a well-known failure of LDA/GGA : underestimation of
band gaps for semiconductors by 50% or more. I'm afraid there is little you
can do about it within wien2k. There are methods that go beyond LDA/GGA
(e.g. GW method) and that correct for this. They are much more
computationally demanding, however, and they are not (yet ?) available in
wien2k.

Stefaan