[Wien] Confusion in Selecting proper value of Hubbard potential.

[Zaid]

Dear Sir,

you are right. Experimental band gap for my compound is 2.0eV. The maximum
band gap on increasing U value for my calculation is 1.117eV at 10 eV. So,
should I increase U value beyond 10eV ? Untill now from my literature
review, the value of U is less than 10 eV.
Secondly, if suppose a compound has not been studied experimentally then
how we choose calue of U ?

Thank you
Zaid


On Sat, Jul 20, 2013 at 1:48 PM, <tran at theochem.tuwien.ac.at> wrote:

> Hi,
>
> I have never heard that the proper value of U is the one when the band gap
> starts to decrease. Usually the value of U is chosen such that the
> calculated properties (e.g., band gap or magnetic moment) agree with
> experiment.
>
> F. Tran
>
> On Sat, 20 Jul 2013, Zaid wrote:
>
> > Respected Users
> >
> >
> > I am applying GGA+U technique to considered compounds. In order to select
> > proper value of U for specific material, I am changing the value of U
> from
> > 2eV to 10eV with a step of 1eV. I was expecting that on increasing U
> value
> > in the range 2-10eV, a value of U will appear where the corresponding
> band
> > gap will start to decrease instead of increase. That value of U where the
> > band gap start to decrease instead of rising will be the proper U value
> in
> > the range 2-10eV.
> >
> > I my case the, every time I am getting increasing band gap values on
> > increasing U value from 2-10eV with a step of 1eV. Band gap does not
> > decrease in the range 2-10eV. Should I increase the range ? May anyone
> > suggest that whether my practice of finding U value is right ? If not how
> > can I find proper value of U for specific compound ?
> >
> > Thank you very much
> >
> > Best Regards
> > Zaid
> >
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