[Wien] Okay to combine mBJ, spinorbit, and LDA+U?

[Kamil Klier]

The Wien example for NiO uses U_eff = 0.52 Ry for the Ni3d orbitals.

Would that mean that using subsequent mBJ potential for 'improvement  
of bandgap of NiO' is not appropriate or at least is an overkill?

Best regards,

Kamil Klier

Quoting Peter Blaha <pblaha at theochem.tuwien.ac.at>:

> mBJ+U is appropriate for 4f systems only (because mBJ is too weak to fully
> localize the 4f electrons). Do not use it for d-electrons.
>
> mBJ is made to give a good bandstructure. We have evidence, that the  
> resulting
> electron density is too ionic, thus a force optimization using MSR1a could
> be problematic (although it could be better than GGA in some cases (with 3d
> electrons - Jahn-Teller distortions).
> Eventually, MSR1a with the original BJ potential (c=1) is physically more
> justified, sind original BJ is an approximation to OEP (optimized  
> effective potential),
> which should be close to the "exact local exchange-only" potential.
> (Note that an "exact exchange potential" + LDA-correlation can be much more
> wrong than plain LDA !!!!! for certain cases, because we miss the  
> error cancellation)
>
> before doing Spin-orbit calculations, I'd remove case.in0_ggr and use the
> case.grr file from the scf-mBJ calculation without SO. I do not trust
> the kinetic energy densities with SO.
>
>
> Am 16.08.2012 22:15, schrieb Laurence Marks:
>> If it is a decent insulator I would do LDA+U directly; often it
>> converges better and since the lattice parameter and forces change you
>> do not gain much by first doing LDA/GGA. Normally LDA+U is stable,
>> often more stable that LDA/GGA. Volume optimization should be done
>> first, then min_lapw or MSR1a. Better is to do MSR1a or min_lapw at
>> each volume.
>>
>> Then add -so, mBJ as appropriate with the optimized positions.
>> However, I not sure if mBJ+U is appropriate (I doubt that it is). It
>> might be that LDA+U positions are a better approximation for mBJ, not
>> sure. One way is to minimize the forces with mBJ using MSR1a (not
>> min_lapw/PORT) and compare them to LDA+U. If they are the same then
>> you are in good shape, needs testing. Maybe someone has....
>>
>> N.B., it is completely fine to minimize positions in mBJ using MRS1a
>> -- do not use min_lapw/PORT, it will not be correct. MSR1a does not
>> care that the energy is incorrect whereas min_lapw/PORT does.
>>
>> On Thu, Aug 16, 2012 at 2:44 PM, Jeff Spirko <spirko at lehigh.edu> wrote:
>>> Is it okay to use spinorbit and LDA+U with mBJ?
>>>
>>> I would guess it is done like this:
>>>  * Check that forces <10 mRy/au with plain LDA or GGA.  Reduce via  
>>> min_lapw.
>>>  * Volume optimization (if desired) with plain LDA or GGA to reduce
>>> absolute pressure.
>>>  * Set up LDA+U (Sec 4.5.6) and use -orb flag from now on.
>>>  * Need to converge LDA+U???
>>>  * Follow mBJ instructions (Sec 4.5.9).
>>>  * After mBJ+LDA+U is converged, follow spinorbit instructions (Sec 4.5.5).
>>>  * For spinpolarized, check whether atoms became nonequivalent
>>> (affects case.inso, case.inorb,
>>>     case.indmc, case.in1c, basically any input file with atom  
>>> lists or indices)
>>>  * touch .fulldiag (necessary because klist can change???)
>>>  * Do final run with -so -orb
>>>
>>> Best regards,
>>> --
>>> Jeff Spirko   spirko at lehigh.edu   WD3V   |=>
>>>
>>> The study of non-linear physics is like the study of non-elephant biology.
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
>>
>>
>
> -- 
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at theochem.tuwien.ac.at
> -----------------------------------------
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