[Wien] confusion with GGA+U and mbj

[shamik chakrabarti]

Dear Prof. Tran and Prof. Blaha,

                                          Thank you for your
elaborate response. I got the point.

Thanks once again.

with regards,

On Sun, 8 Mar 2020 at 16:10, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> It really depends on the specific example if you need to be carefully
> with the starting point, since both, LDA+U and mBJ can give multiple
> solutions in certain cases.
>
> Eg: MnO or NiO do not require any special care. The dominant cubic
> crystal field is sufficient to drive the correct solution and both,
> GGA+U and mBJ will give only one solution, independent on the starting
> conditions.
>
> Very different is eg. FeO: Both, GGA+U and in particular mBJ will NOT
> give a band gap when started with plain GGA (and probably also not when
> starting from scratch using atomic densities ??)
>
> An analysis of the partial Fe-DOS is necessary, followed with a
> reoccupation of the density matrix by hand to occupy the proper single
> orbital. Using this starting dmat-files, GGA+U gives an insulator (and
> this solution should have lower energy - depending on U). Continuation
> with mBJ from such a solution, also gives a nice band gap.
>
> Analyse your partial TM-d state DOS !
>
> Am 08.03.2020 um 11:25 schrieb Tran, Fabien:
> > Hi,
> >
> > It is recommended (but not mandatory) to do first a GGA calculation
> > before using GGA+U or mBJ. By doing so, the starting electron density
> > for the GGA+U/mBJ SCF iterations may be better than the one
> > from init_lapw (lstart/dstart) in order to reduce the number of
> > iterations and/or to reach the proper ground state.
> >
> > It may also be a good idea (but again not mandatory) to start a mBJ
> > calculation using the GGA+U electron density.
> >
> > FT
> >
> > ------------------------------------------------------------------------
> > *From:* Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of
> > shamik chakrabarti <shamik15041981 at gmail.com>
> > *Sent:* Sunday, March 8, 2020 10:09 AM
> > *To:* A Mailing list for WIEN2k users
> > *Subject:* [Wien] confusion with GGA+U and mbj
> > Dear Wien2k users,
> >
> >                             If simulation of a material is to run with
> > GGA+U to get an approximate band gap, then *whether GGA+U or GGA* has to
> > run as a first step for running mbj?
> >
> > As user guide says that we have to run a normal SCF prior to mbj, my
> > confusion is whether the normal SCF is to run with GGA or GGA+U if U is
> > mandatory for the material.
> >
> > Looking forward to your response in this regard.
> >
> > with regards,
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> > _______________________________________________
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> >
>
> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
> WWW:
>
> http://www.imc.tuwien.ac.at/tc_blaha-------------------------------------------------------------------------
>
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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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