[Wien] Query regarding Hubbard U for Ti in TiO2

[shamik chakrabarti]

Dear Karel,

            Thank you so much for your mail. It would be very helpful.

with kind regards,

On Tue, 23 Feb 2021 at 02:05, Karel Vyborny <vybornyk at fzu.cz> wrote:

> Dear Shamik,
> it is perhaps a better idea not to try to _calculate_ the U but rather,
> use the arguments of the Hu&Metiu article you mentioned (J Phys Chem C
> 115,
> 5841) for either hybrid functionals or GGA+U with values Hu&Metiu argue to
> give a reasonable gap, reaction energies etc. A quick GGA calculation for
> TiO2 shows that already within the sphere of Ti atoms, there's
> significantly
> more than 18 electrons (which would correspond to nominal Ti^4+) so it is
> wrong to think about ni=nj=0 (in terms of what you write below). If you
> wish to convince yourself (personally, I'm all in for being skeptical!)
> that some particular GGA+U calculations make sense, try comparing more
> physical quantities (optical or photoemission spectra for example) to
> anything that is available on the experimental side.
>
> Best regards,
>
> Karel
>
>
>
>
> --- x ---
> dr. Karel Vyborny
> Fyzikalni ustav AV CR, v.v.i.
> Cukrovarnicka 10
> Praha 6, CZ-16253
> tel: +420220318459
>
>
> On Fri, 19 Feb 2021, shamik chakrabarti wrote:
>
> > Dear Wien2k users,                                I am interested in
> > calculating the reaction energy for the equation
> >                         2 TiO2 + H2 = Ti2O3 + H2O
> > In this case, I should use U for Ti in Ti2O3. However, in
> earlier research
> > works it has been given that the same U should also be used for Ti in
> TiO2.
> >
> > My query is as Ti exists as +4 state in TiO2 why at all we need to use U
> for
> > it?
> >
> > We know EU = U/2 SUM (ni, nj), however as ni & nj is zero for Ti in TiO2
> why
> > should we also need to use U for Ti in TIO2?
> >
> > Waiting forward to your response. Thanks in advance.
> >
> > with regards,
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
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-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
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