[Wien] band gap for structure with a defect

[Peter Blaha]

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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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email: peter.blaha at tuwien.ac.at
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