[Wien] LDA+U changed between the versions?

[Jian-Xin Zhu]

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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