[Wien] Okay to combine mBJ, spinorbit, and LDA+U?
Peter Blaha
pblaha at theochem.tuwien.ac.at
Sat Aug 18 19:12:45 CEST 2012
Read the paper
Am 18.08.2012 18:59, schrieb Jameson Maibam:
> Dear sir, please suggest suitable exchange correlation for ZrO2 in monoclinic structure. Its reported band gap using GoWo is 5.34eV . My experimental groups got 5.5eV.
> Yours sincerely
> Jameson Maibam
>
> ----- Original Message -----
> From: Peter Blaha <pblaha at theochem.tuwien.ac.at>
> To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
> Cc:
> Sent: Saturday, 18 August 2012 10:15 PM
> Subject: Re: [Wien] Okay to combine mBJ, spinorbit, and LDA+U?
>
> Yes, the Zn-3d states are very localized (like the 4f) and some U (much smaller than what you would use in GGA+U)
> will give you the experimental gap.
>
> Alternatively you can use modified mBJ parameters (PRB 85, 155109) which are tailored more towards semiconductors
> (gaps below 5 eV) and bring the ZnO gap above 3.2 eV.
>
> Am 18.08.2012 18:27, schrieb Kamil Klier:
> > Thanks Fabien,
> >
> > Indeed the match between MBJLDA theory and experiment (Fig. 1 in the quoted paper) is excellent.
> >
> > However, the bandgap of ZnO is underpredicted by mBJ only, reading from Fig. 1 ca. 2.8 eV. This would render zinc oxide colored in the visible region, but pure ZnO is
> > white, in accord with experimental bandgap 3.2 - 3.4 eV. Moreover, the Zn3d_10 (filled) narrow band falls below the O2p valence band (from VB XPS) while a quick
> > calculation with MBJLDA results in blending of O2p and Zn3d. Is it possible that in the ZnO case the U (say U_eff = 0.46 Ry) would help a bit as follows: it would push the
> > Zn3d down and improve the bandgap - unless of course there are theoretical reasons why mBJ and U should be in conflict. That does not seem to be the case, however, for 4f
> > orbitals.
> >
> > Best regards,
> >
> > Kamil Klier
> >
> > Quoting tran at theochem.tuwien.ac.at <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto:pblaha at theochem.tuwien.ac.at>
> >>> >-----------------------------------------
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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 <mailto:pblaha at theochem.tuwien.ac.at>
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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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