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I calculated the bandgap for one system in the unit cell and in the supercell of 2x2x1 and 3x1x1. Although 3x1x1 gives the same bandgap as I got from the unit cell (1.79 eV) but 2x2x1 is giving 1.75 eV. I kept all input file settings same in all the supercells as in-unit cell including K- POINTS. I observed this bandgap by plotting the dos. I think the bandgap should remain the same in the supercell. Any suggestion will be very helpful.

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  • $\begingroup$ To avoid clutter, comment discussion has been moved to chat $\endgroup$
    – Tyberius ♦
    Nov 8, 2021 at 15:39

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First off, those values are pretty close, probably within the accuracy of your method (I assume DFT). Notice that you state all input parameters stay the same except that cell size. However, some parameters are changing. In this case, it's the k-point density. Simulations with different cell sizes, but same k-point mesh, will have different k-point densities. So I'm guessing that's what's causing the slight difference.

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  • $\begingroup$ After lots of effort, I am not able to get the bandgap in the supercell of 2x2x2 and 2x2x1 same as in the unit cell and in the 3x1x1 supercell, still 0.04 eV difference I am observing. I tried with the different K mesh but nothing works out. $\endgroup$
    – poonam sharma
    Nov 24, 2021 at 17:46

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