I performed an HSE06 calculations using VASP and the calculated band gap is in good agreement with experiment. However the band is not smooth, with very sharp, zig-zag like features. How to improve the smoothness of the band structure?
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1$\begingroup$ I think that you need to change the number of k-points you are using in your path between the high symmetry points at the Brillouin zone. $\endgroup$– Camps ♦May 18, 2020 at 11:50
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$\begingroup$ User CKI asks (but doesn't have enough rep to write a comment): "Could you post the KPOINTS file? I suspect that you eventually do not use an actual path." $\endgroup$– Nike DattaniMay 24, 2020 at 17:47
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$\begingroup$ Adding to what I.Camps said, your problem is either: i) The plane wave cutoff - You need to test convergence with respect to this. If you want to avoid the convergence test, you can take 1.3*Emax in VASP, which is what is recommended. ii) K-point grid - There is no work-around to testing convergence wrt this. There are some general guidelines(use even no. of K points etc).. iii) Smearing: If your material has a gap more than say 0.2-0.3 eV, then you don't need to worry about this. Finally, your method of generating band structures can also be at the heart of the problem - How did you do it? $\endgroup$– Xivi76Jun 13, 2020 at 18:47
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Normally, this could happen due to several issues:
- discontinuity in the k-path you selected to calculate the band structure,
- low number of points in each interval,
- bad convergence parameters.
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$\begingroup$ perhaps add that the number of points in each interval could be matched against the distance in the reciprocal cell. Say a 2D lattice with a long (few) and short (many) direction (points in interval). Often I see people use the same number of points in each interval which might not always be the best idea for extremely skewed lattices. $\endgroup$ Sep 14, 2021 at 8:54