Dear Matteo Thanks?many for your reply. But my special case is for the defect states (has d-character? )in TiO2 that is in resonance with conduction band and is filled with 2 electrons. When I increased the U from 1 to 4 I saw that the defect state bieng pushed up instead lowering of this state as we expected from theory of LDA+U. Is it true? Moreover?for another defect state that is empty and is above conduction band I saw it? being peshed down in contrast with LDA+U expection. But when I perform GW@ GGA+U I see that the behavior is reversed in which empty states?being pushed up while filled state is?pushing down. what does it mean??is it rational? thanks a lot
Ali Kazempour Fritz-Haber-Institut fax : ++49-30-8413 4701 der Max-Planck-Gesellschaft Faradayweg 4-6 e-mail: kazempou at fhi-berlin.mpg.de D-14 195 Berlin-Dahlem / German --- On Sun, 7/4/10, Matteo Cococcioni <matteo at umn.edu> wrote: From: Matteo Cococcioni <[email protected]> Subject: Re: [Pw_forum] LDA+U character To: "PWSCF Forum" <pw_forum at pwscf.org> Date: Sunday, July 4, 2010, 8:29 PM dear Ali, I will try to answer your questions ali kazempour wrote: > Dear All > I have some questions about LDA+U nature. Does U treate like a? > perturbation( I know that GW( many body peturbation method) is > modified version of LDA+U? if yes why we are allowed to take > U=0,1,2,........ up to large values? and why we solve system > self-consistent? > no, U is not treated as a perturbation. it is more a correction to the "standard" DFT energy functional. you can check the relationship between +U and GW in the following reference (probably there are many more): Anisimov et al, Journal of Physics: Condensed Matter 9, 767 (1997) > Does U comute with KS-hamiltonian in every U values? I mean? does the > order of states remains intact with respect to LDA or they can change? > and final question: > For sure the +U correction to the potential commutes with the translation and other symmetries of the crystal. I think it doesn't commute with the rest of the Hamiltonian (the unperturbed DFT one). So if you think to switch on the U from a U=0 ground state, unless the KS states are already bloch sums of atomic orbitals (that would be a very unlikely accident) the +U correction introduces interactions between them if allowed by symmetry and you are going to get a non trivial mixing of them besides a shift in the eigenvalue. Probably the most significant modifications are going to take place for states around the Fermi level that may get more localized. The ones that are deeper in energy are probably closer to be atomic-like already and they will, at most, get a shift in the corresponding eigenvalues. > What is the effect of U on > 1-empty states in conduction band? (with d-character) > pushed up > 2-half filled states in conduction band(with d-character) > depends: see above > 3-filled- states in conduction band (with d-character) > pushed down > Thanks a lot > > > Ali Kazempour > > hope this helps. Matteo > > Fritz-Haber-Institut fax : ++49-30-8413 4701 > der Max-Planck-Gesellschaft > Faradayweg 4-6 e-mail: kazempou at fhi-berlin.mpg.de > D-14 195 Berlin-Dahlem / German > > > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >??? -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Matteo Cococcioni Department of Chemical Engineering and Materials Science, University of Minnesota 421 Washington Av. SE Minneapolis, MN 55455 Tel. +1 612 624 9056? ? Fax +1 612 626 7246 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100706/c2004328/attachment.htm
