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: > >> 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. >>> > > >_______________________________________________ >>> > > >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 >>> >----------------------------------------- >>> >_______________________________________________ >>> >Wien mailing list >>> >Wien at zeus.theochem.tuwien.ac.at >>> >http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>> > >>> >>> >>> >>> ---------------------------------------------------------------- >>> This message was sent using IMP, the Internet Messaging Program. >>> >>> _______________________________________________ >>> Wien mailing list >>> Wien at zeus.theochem.tuwien.ac.at >>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >>> >> _______________________________________________ >> Wien mailing list >> Wien at zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> > > > > ---------------------------------------------------------------- > This message was sent using IMP, the Internet Messaging Program. > > _______________________________________________ > 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 -----------------------------------------
