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

[Peter Blaha]

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.
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>
>
>

-- 
-----------------------------------------
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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