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

[tran at theochem.tuwien.ac.at]

Yes, mBJ alone is already ok for NiO:
http://prl.aps.org/abstract/PRL/v102/i22/e226401
So, adding U is not a good idea.

On Sat, 18 Aug 2012, Kamil Klier wrote:

> 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.
> > > >_______________________________________________
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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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