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Matter Modeling

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  • $\begingroup$ Provided both calculations are sufficiently converged in all computational parameters you should get the same band gap. It is the same substance after all. (caveat, I don't know what you mean by a "nscf calculation", I'm assuming you mean a standard SCF - please avoid code specific terms if at all possible) $\endgroup$ Commented Jan 2, 2022 at 9:48
  • $\begingroup$ @IanBush It's non self consistent field calculations with tetrahedra smearing to get highest occupied and lowest occupied energy levels. I will edit it in the question. ok thank you, the calculations are converged. So there must be something wrong, I should do it again. $\endgroup$ Commented Jan 2, 2022 at 10:04
  • $\begingroup$ @epsilon02fft Try comparing SCF calculation of both instead, or better their band structures. NSCF calculations are kind of like extrapolating the wavefunction from SCF to a denser mesh. Therefore, I don't think changing any inputs between SCF and its subsequent NSCF will give you any meaningful data. $\endgroup$ Commented Jan 3, 2022 at 11:14
  • $\begingroup$ Your non-self-consistent calculation has to have a sufficiently dense grid. You have to check this by using a convergence method and systematically increasing the sampling (kpoints or reciprocal sampling if you are using a plane-wave code). Then when you are having the supercell are you running the scf again? In a supercell depending on the ordering of the alloying your lattice parameters might be different which can result in a different bandgap. $\endgroup$ Commented Jan 5, 2022 at 4:14
  • $\begingroup$ @TaraMishra Yes. I will perform it again. Then I will update here. $\endgroup$ Commented Jan 8, 2022 at 11:46