VBM in charged defect formation energy

[exenGT]

Hi,

In the tutorial for calculating charged defect formation energy (http://docs.quantumwise.com/tutorials/charged_defects/charged_defects.html), the functional PBEsol is used. However, we know that in general GGA doesn't give correct band gap and band edge positions. So is it okay to use the VBM calculated using PBEsol, or is it necessary to go to MGGA to account for possible errors?

Thanks!

[Ulrik G. Vej-Hansen]

The energy wrt. vacuum of the occupied states is normally quite good for GGA, even though the band gap is off. As MGGA does not give usable total energies, it is not really an option in this case, as we need both VBM and total energy calculated with the same absolute reference.

[exenGT]

Thank you very much for your helpful response!