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
_______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) users mailing list [email protected] https://lists.quantum-espresso.org/mailman/listinfo/users
