I am doing DFT calculations using Quantum Espresso. But I am uncertain about a couple of things before doing massive ground-state calculations so that I can safely go with Yambo BSE steps because these variables also appear in Yambo keywords so I wanted to have them right from the ground state!
Q1: I'm modeling a semiconductor with a well-defined bandgap (DFT is predicting a very close value after applying corrections). Now, I have also introduced doping that will be for sure either p-type or n-type. Moreover, due to semiconductor, I am using the keyword
Code: Select all
occupations = "fixed"
...
I think due to addition or deficiency of charge QE is trying to force me to have some sort of smearing and degauss. Right? But after applying some fictitious temperature (degauss value) the fermi position will change. In the fixed occupation, the Fermi level is just at the top of VB (as it should) and in smearing case it is in around the middle. Therefore, how I will be able to relate with pure bandstructure case? My purpose is to lower the bandgap after doping and make conclusions on the basis of the movement of Fermi level, but here fermi level is moving due to smearing too instead of just dopants.Error in routine electrons (1):
charge is wrong: smearing is needed ...
2: I have not used nspin parameter despite Oxygen and other transition metals in the system! Actually, the system total energy was not changing when nspin was 2. Moreover, I have also not used spin-orbit interactions despite having W (Tungsten)and Bi (Bismuth) in the system! Does Yambo consider theses parameters for excited-state calculations?
4: To correct the bandgap I applied Hubbard parameter (DFT+U) but the system total energy is increasing as I am applying U values to single or both the atoms in the system! Is it okay? (I know Yambo will discard U parameter for generating the database).
Regards,
Haseeb Ahmad
MS -Physics
LUMS, Pakistan