[Wien] LDA+U changed between the versions?

[Laurence Marks]

One important addendum. If LDA+U is unphysical, it may not converge
and nothing you do will make it! I ran into something like this some
time ago when I tried PBE0 for a Ni surface.

Unless you run into a (rare) bug in Wien2k, failure to converge or
poor convergence is an indicator that the physics has been posed
wrong.

2010/8/3 Jian-Xin Zhu <jxzhu at lanl.gov>:
> Igor,
> Thanks for the suggestion.
> For the compound I am faced with, Ce127, I treated 4f as  localized states
> first by following the instruction given in
>
> WIEN2k-FAQ: "open core" treatment of 4(5)f electrons
>
> and the procedure worked fine.
> But I also noticed the comment
> "A better approach would be to use LDA+U, which is available in WIEN2k."
> I then had to fight with the whole business of the convergence problem.
> As for Ce in the compound being mixed valence state or not, how can we
> decide a priori?
> The conventional LDA calculation always puts the Ce 4f close to the Fermi
> energy,
> yielding a fractional occupation.
> I appreciate if you can share more of your experience.
> You are right. The LDA+U to iron pnictides is unphysical because they are
> metallic.
> I simply used it to find out why the LDA+U does not work for Ce systems.
>
> Laurence,
> I just copied the two files you pointed from 10.1 into 9.2 SRC_mixer folder,
> and will report again what I can obtain.
>
> Best regards,
> Jianxin
>
>
>
>
>
>
>
>
> On Aug 3, 2010, at 8:52 AM, mazin wrote:
>
> Laurence,
>
> Thanks for your comments. It is a good idea to download a newer version
> anyway, but unfortunately my problem is of different sort. I can converged
> to the machine accuracy both calculations, WIEN2k_07 and WIEN2k_09, and the
> results are physically different. I have no problem with convergence in
> either case, and can verify manually that both calculations are fully
> converged. The problem is therefore unrelated to a possible bug in the
> mixing scheme.
>
> Jianxin,
> Ce in some compounds is in mixed valence state or close to that. In those
> cases, you may have problems with convergence, and you should be careful
> fighting these problems, because even if you manage to converge the
> calculations, that may be a rather unphysical solution. In CeTe3 Ce is not
> close to mixed valency so there is no problem with convergence. Neither
> should there be any with pnictides, assuming you are talking about U on Fe,
> except that LDA+U is completely unphysical for these materials.
>
> Igor
> --
> **********************************************************************
> Igor Mazin, NRL, code 6390, 4555 Overlook Ave SW, Washington, DC 20375
> Phone: (202) 767-6990; Fax: (202) 404-7546; e-mail mazin at nrl.navy.mil
> Home Page http://cst-www.nrl.navy.mil/users/mazin
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-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Electron crystallography is the branch of science that uses electron
scattering and imaging to study the structure of matter.