[Wien] band gap for structure with a defect

[Natalia Andreeva]

Thanks a lot

On Wed, Sep 13, 2023 at 8:56 PM Peter Blaha <peter.blaha at tuwien.ac.at>
wrote:

> 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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-- 
Best Regards,
Natalia Andreeva.
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