Hello,
i run the scf file for band calculation. I know that calculated materials is semiconductor with 1 eV -2 eV band gap.. But after scf calculation, highest and lowest energy level was same value as a highest occupied, lowest unoccupied level (ev): 6.9836 6.9836. Its mean that the band gap is not occur. But the calculated material is semiconductor. Where could i be doing wrong ?
Best
Dear Merve Özcan,
I believe you should try to add some more material to this discussion. First of all, is the band gap calculated or measured? That is there is an experiment or you are trying to reproduce some calculation?
In the case this value is experimental, did you look in the literature to see if there is an equivalent calculation performed? In the positive, did you try to redo the same calculation by using the same parameters? (I mean the same pseudopotentials, with the same or similar cutoffs and convergence parameters?) If the value you quote is numerical, did you try to perform the same calculation?
Consider that standard DFT notoriously reduces the band gap of semiconductors. This effect originates from the fact that DFT tends to delocalise the electrons thus reducing the band gap.
I hope this helps,
Roberto
Hello all.
You may have been following some tutorials you see around internet. From SCF calculations, it's difficult to measure bandgaps, but for semiconductors we can estimate. Try this:
- in your input file, put "occupations = fixed"
- determine the number of bands, and put few more bands than you have for ground state.
Check if this works, and send a reply. And DFT underestimates bandgaps values, as @Roberto D'Agosta said, so keep it in mind.
Best regards,
Ricardo Tadeu
thank you for your replies Ricardo Tadeu Maia and Roberto D'Agosta . i changed the occupations=fixed and also i obtained different value highest and lowest energy level. Thus, band gap occurs. Many thanks
The other possibility is to include occupation=smearing but decrease the value of the degauss...
Regards,
Roberto
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators