Solution for unsatisfactory GW-corrected band-gap in GaAs before BSE
Posted: Tue Feb 27, 2024 3:45 pm
Dear Yambo code developers,
I want to get a satisfactory GW-corrected band-gap energy in bulk GaAs, whose experimental value is 1.4 eV. To that end, I have been using QE + Yambo codes. As I have read in literature, this exercise turns out to be problematic when using standard LDA or GGA pseudopotentials (PPs) and it is recommended to have a DFT-starting point based on hybrid PPs.
Nevertheless, I would like to avoid the use of such computationally heavy PPs. I have been doing some calculations with PPs within LDA (PZ) and GGA (PBE & PBEsol) from the Optimized Norm-Conserving Vanderbilt (ONCV) PP database (Ga: 3d10 4s2 4p1 Zval=13 & As: 4s2 4p3 4d0 Zval=5) for which I get DFT band-gaps in the range of 0.33-0.53 eV and GW-corrected values around 0.75-0.79 eV. On the other hand, I have constructed PPs using the ld1.x tool from QE in order to take explicitly into account 3d10 electrons of As as valence electrons in the PP for the same three approximations of the XC and I get DFT band-gaps in the range of 0.23-0.45 eV and GW-corrected values around 1.03-1.05 eV. It seems that more core electrons you take into account better you approach to the experimental value, but it is not yet enough.
So my question comes now: In order to get a subsequent BSE calculation, the scissors shift I use in the BSE solver must be the one that recovers a value of 1.4 eV. Nevertheless, for the static screening should I also use it or not? I would say no, as in a BSE calculation on top of GW QP bands the static screening corresponds to the RPA from DFT, and here the BSE calculation would be on top of scissors shifted QP bands, so similar staff in practice. Is not it? If not, which is the best way to proceed in these cases? Please, feel also free to recommend me any other strategy I have not thought about.
Thank you in advance for your answer and advices.
Peio.
I want to get a satisfactory GW-corrected band-gap energy in bulk GaAs, whose experimental value is 1.4 eV. To that end, I have been using QE + Yambo codes. As I have read in literature, this exercise turns out to be problematic when using standard LDA or GGA pseudopotentials (PPs) and it is recommended to have a DFT-starting point based on hybrid PPs.
Nevertheless, I would like to avoid the use of such computationally heavy PPs. I have been doing some calculations with PPs within LDA (PZ) and GGA (PBE & PBEsol) from the Optimized Norm-Conserving Vanderbilt (ONCV) PP database (Ga: 3d10 4s2 4p1 Zval=13 & As: 4s2 4p3 4d0 Zval=5) for which I get DFT band-gaps in the range of 0.33-0.53 eV and GW-corrected values around 0.75-0.79 eV. On the other hand, I have constructed PPs using the ld1.x tool from QE in order to take explicitly into account 3d10 electrons of As as valence electrons in the PP for the same three approximations of the XC and I get DFT band-gaps in the range of 0.23-0.45 eV and GW-corrected values around 1.03-1.05 eV. It seems that more core electrons you take into account better you approach to the experimental value, but it is not yet enough.
So my question comes now: In order to get a subsequent BSE calculation, the scissors shift I use in the BSE solver must be the one that recovers a value of 1.4 eV. Nevertheless, for the static screening should I also use it or not? I would say no, as in a BSE calculation on top of GW QP bands the static screening corresponds to the RPA from DFT, and here the BSE calculation would be on top of scissors shifted QP bands, so similar staff in practice. Is not it? If not, which is the best way to proceed in these cases? Please, feel also free to recommend me any other strategy I have not thought about.
Thank you in advance for your answer and advices.
Peio.