In addition to what Igor said:
If you want a reasonable gap for the bulk, you can use mBJ+U (with a
small U of a few eV).
Still, for your cell, you won't get an insulator (also doped Si is
"metallic" and conducting, otherwise a computer would not work ...).
PS: Draw the DOS and compare with the undoped DOS. Maybe you understand
then better.
Am 13.09.2023 um 19:19 schrieb Natalia Andreeva:
Dear WIEN2k users,
I am calculating the band gap of bulk BaTiO3 using the LDA+U with PBE
functional. For the values below, the band gap was 2.002 eV (which I
can explain by the choice of the PBE functional). When I moved to a
supercell with a defect (oxygen vacancy, supercell dimensions 2x2x1),
the band gap became 0.0 eV.
I tried to increase the Hubbard parameter U. For example, for bulk
calculations with U=1.121 Ry = 15.252 eV, the band gap was 3.391 eV.
However, running with the same parameters for a supercell with a
defect gave a calculated value of 0.889 eV.
I have the following questions:
1. Why does the band gap decrease so much when going from bulk to
supercell with a defect?
2. Is it worth changing the PBE functional to another one if the band
gap for bulk is less than the experimental one?
3. If I continue the calculations on PBE+U, how can I improve the values?
With Best Regards,
Natalia
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