QP gap of black phosphorus

[burkzdemir]

Dear developers,

I am trying to calculate G0W0 gap of black phosphorus. I converged the result with respect to total number of bands (200), response block size (450 RL), and I used 4 valance and 5 conduction bands. However, I find 0.74 eV with G0W0 (PBE value is 0.17 eV) and in the literature, G0W0 gap is found to be 0.3 eV. Experimental value is 0.33 eV. Why am I finding so large gap? Am I missing something in the calculations?

[Daniele Varsano]

Dear Burak,
probably you are doing nothing wrong BP is rather complex as the gap is very sensible to the considered structure, in particular the interlayer distance.
From the number you are obtaining it seems like you are not considering vdW interaction in the structure and it turns out the system has a rather large gap.
Note that when considering relaxed structure using vdw interaction you obtain an interlayer distance which is in agreement with experiments but the PBE band structure has a very small band gap, or even metallic behaviour. GW on top of this band structure provides results in agreement with experiment, but for my experience only if you consider some eigenvalue sellf-consistency. There are in literature calculation reporting a band gap in agreement in the literature at G0W0 level, but we were not able to reproduce and this is most probably due to the different plasmon pole model used in the calculation (Tran et al. PHYSICAL REVIEW B 89, 235319 (2014)).

You can find some info in: Ridenko et al Phys. Rev. B 92, 085419 (2015) and reference therein.

Best,

Daniele