Dear Prof. Matteo Cococcioni, Thank you very much for explanation, it helps me a lot. According to the document of pw input file, rotational invariant DFT+U is implemented in pw now, with lda_u_type=1. I think my input files are correct, when I use rotational invariant DFT+U and DFT+U+J you developed.
I hope you can understand that my hesitation to put data I don't understand on a public place. I can describe my problem. It seems to be related to the question why U_eff=U-J is valid. I have two spin states of a transition-metal ion. As you know, U favours high-spin state, and conventional wisdom tells us J should favours high-spin too. It is easy to understand why in simplified DFT+U, J does the opposite, since it is just a reduction of U. I expected, by fully rotational invariant DFT+U, J favours high-spin energetically. But, in my calculations, rotational invariant DFT+U behaves just like the its' simplified version. Only the DFT+U+J method shows the right trend. If DFT+U+J is just a simple version of rotational invariant DFT+U, I still don't know why rotational invariant DFT+U fails for this particular problem. I also don't think U_eff=U-J has too much physics ground, but, in calculations, it seems to be true... Any comment on this topic is very welcome. Bests Jia On Tue, Mar 18, 2014 at 5:39 AM, Matteo Cococcioni <matteo at umn.edu> wrote: > > Dear Jia, > > when we did the work you cite (the PRB paper on CuO) we understood we > needed to have explicit magnetic interactions in the +U functional, but we > tried to understand if there were simpler ways to add it than using the > otationally invariant implementation of DFT+U. On the other hand the > simpler version of it by Dudarev et al (PRB 98) was too simple as it > reduces the role of J to a mere reduction of the effective U (that is, > U_eff = U-J). To be honest, this latter point I have never fully > understood: one gets the simpler version of the +U correction by setting J > = 0 in the fully rotational one, so I don't see how one could end up with > an effective U that is U-J. Anyway, what we tried to do was to re-analyze > the approximation the simpler version is based on (in the limit where U_eff > does actually result to be equal to U-J) and to check whether or not other > terms of the same order were arising. And it seems to us that an extra one > needed to be added. > > I will try to clarify specific questions of yours below. > > > On Tue, Mar 18, 2014 at 3:07 AM, Jia Chen <jiachenchem at gmail.com> wrote: > >> Dear all, >> >> I am working on molecule with localized d electrons and two different >> spin states, especially correlation due to Hund's coupling J at this >> moment. I tried the DFT+U+J method (PRB 84, 115108, 2011) implemented in >> Quantum Espresso, and found out the J dependence is quite different from >> the rotational invariant DFT+U (PRB 52 R5467, 1995). >> > > > first of all: make sure you are using Hubbard_J0 (lda_plus_u_kind = 0). > the Hubbard_J relates to the non-collinear implementation and I'm not sure > what it does in case of nspin = 2. Although I didn't participate to this > implementation, I believe that it might reduce to the fully rotational > implementation, but I'm not sure and other people can confirm. > > > >> I am surprised by the results, because rotational invariant DFT+U has >> full coulomb interaction parametrized by Slater integrals, Hund's coupling >> J show up in anisotropic and spin polarized interactions. As a model, it >> covers both Hund's first and second rule. Theoretically, I don't know >> what's missing in this method. >> >> > > see above and below. > > > >> Apparently, developers of DFT+U+J know how to go beyond rotational >> invariant DFT+U. I read the paper, but still don't understand the idea >> behind it. I would like to ask two questions: >> 1. What is not right in rotational invariant DFT+U, as a Hartree-Fock >> level theory regarding J? >> > > > the fact that it is Hartree-Fock level of theory. In fact, as we wrote in > the paper, the extra term we added is beyond HF in the sense that it cannot > be captured supposing that the many-body wave function consists of a single > Slater determinant. > > > >> 2. How DFT+U+J improves rotational invariant DFT+U, just in general? >> > > > we didn't compare the two. but if you end up doing please report the > results on this forum. > > Hope this helps. best, > > Matteo > > > >> >> Appreciate your help! >> >> Cheers >> -- >> Jia Chen >> Postdoc, Columbia University >> >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Jia Chen -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140318/4dc5c750/attachment.html
