[QE-users] Different band gap in unitcell and in supercell

[poonamsharma]

Dear users,
I am trying to calculate 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 (1.80 eV) but 2x2x1 is giving 1.75 eV. I kept the
input files settings same in 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.
Is this 1.75 eV is acceptable.
Also in order to match this bandgap with the experimental value, I applied
the U parameter. In unit-cell with different U values, I got a variation in
band gap that I am expecting but in supercell, bandgap remains the same, no
variation observed.
I'll be very thankful for any suggestions.

Thanks and regards,
Poonam Sharma



-------------------------------------------------------------------------------------------------
Poonam Sharma
Research Scholar
Department of Physics
Indian Institute of Technology Bombay
Mumbai - 400076
India.
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