Dear Jia, see below.
On Wed, Mar 19, 2014 at 4:31 AM, Jia Chen <jiachenchem at gmail.com> wrote: > 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. > > our DFT+U+J is the one you get with hubbard_u_kind = 0 and Hubbard_J0 =/= 0. > 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. > As I wrote yesterday in my email DFT+U+J0 is NOT a simpler version of the rotational invariant DFT+U. if you simplify the rotational invariant DFT+U you obtain the dudarev DFT+U, possibly with U_eff = U-J. best, Matteo > > 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 > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140319/e7cd6272/attachment.html
