[QE-users] [SUSPECT ATTACHMENT REMOVED] RE1: Exact band-gap of silicon

[Lucas Nicolás Lodeiro Moraga]

Hi!
First just some fundamental things:
The band gap of silicon is an indirect gap between Gamma VBM and X (or near
X) CBM, with ~1.2 eV. If you see the difference between VBM and CBM at
Gamma point (direct band gap), the band gap is around 3 eV.
The Kohn-Sham-GGA (or LDA) level of theory underestimates the band gap of
solid systems, it is a fact. The pseudo potential does not fix it at all.

If you want to improve the band gap, you need to use a hybrid functional o
high level as GW. HSE understimates a little bit and PBE0 subestimate a
little bit the band gap. PBE0(alpha) could be better.

As an example I adjunct an examples calculations with GGA, hybrid
calculations a G0W0 calculations over it. They are just reference, because
I use a primitive cell only with Gamma point, then the direct band gap is
the only thing you can see. For a real calculation, a bigger cell or more
kpoints are needed. This would complicate a hybrid or G0W0 calculations due
to the resources.

Regards
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