[Wien] confusion with GGA+U and mbj

[Peter Blaha]

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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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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