[Wien] LDA+U
Saeid Jalali
s_jalali_a at yahoo.com
Wed Jul 26 12:20:27 CEST 2006
Thank you for your comments. I am sure you will be happy if know about the following website:
http://www-als.lbl.gov/als/science/sci_archive/57rixs.html
For example, there is by no means a direct relation telling if U is zero then electrons are delocalised.
You may be partially right, but not that way. There is no experiment that is able to measure U and there is no method to calculate U ab-initio! There are only methods to estimate U from both experiment and calculation by some approximations.
Ciao
Gerhard
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Von: wien-bounces at zeus.theochem.tuwien.ac.at im Auftrag von Saeid Jalali
Gesendet: Mi 26.07.2006 00:20
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] LDA+U
Performing careful experiment can answer if a system, i.e. in your case a pure metal, is highly correlated or not at a given thermodynamic state. If this were (not) so and you know it from experiment LDA+U is (not) necessary. If you do not know it and (or) would theoretically investigate (confirm) it, then performing LDA+U assuming U as an variable seems to be an appropriate tool. Since if you find zero value for U comparing your result with experiment, then you can confirm that it is not strongly correlated system. One can investigate utilizing the constraint method of calculating U value the degree of localization. If U is calculated to be zero then the system is predicted purely theoretically to be delocalized. Screening is a good point that you have touched it. But I suggest to be careful about your interpretation taking correct model into account:
The d/f-electrons interact either indirectly as described by the RKKY model within the conduction electrons, where the spins of the d/f electrons are coupled together by the magnetization induced in the conduction electrons, or directly with the other delocalized conduction electrons in the vicinity of the Fermi level as described by the Kondo model, where spin-flip scattering between magnetic d/f electrons and nonmagnetic conduction electrons play more important role than the indirect RKKY interactions of d/f moments.
If you would correctly interpreter your result you may know about these two model Hamiltonian reading many-body text books.
Say hello to everybody there.
hamad at fhi-berlin.mpg.de wrote: Thanks Saeid,
but as we know that LDA+U is needed for systems with strong
electron-electron interaction, this appears in transition metal
oxides that causes the wrong prediction of metallic type rather
than insulator "Mott-Hubbard insulators".
So what about pure transition-metal systems, I think in this case the
screening effect reduces the electron-electron interaction and in this
case LDA+U is not needed. Am I right??
Thanks
Bothina
> Yes, it is meaningful. LDA+U is intended to improve L(S)DA weakness
> of treating strongly correlated f/d density of states. Magnetic
> systems will be non-magnetic in higher temperature. In higher
> temperatur,
those systems again have their d/f states which need
> (sometimes) improvement including LDA+U. However, in practice as
> mentioned in the textbook it is necessary to be treated magnetically
> even non-magnetic systems. This can be done as discussed in the
> usersguide and frequently in the list using runsp_c_lapw script
> (instead of run_lapw) to constrain to be zero the magnetic moment:
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2006-March/006863.html
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2005-October/005994.html
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2004-April/002425.html
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2005-December/006304.html
>
> Bothina Hamad wrote: Dear Wien users,
> I want to ask if is it possible to use LDA+U method in
> a nonspin-polarized calculations? does it have a meaning?
> Best regards
> Bothina
> --
> -----------------------------------------------------------------------
> Bothina Hamad Phone: (+49 30) 8413-4851
> Fritz-Haber-Institut Fax: (+49 30) 8413-4701
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> D-14195 Berlin (Germany) E-Mail: hamad at fhi-berlin.mpg.de
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> Saeid Jalali Asadabadi,
> Department of Physics, Faculty of Science,
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Sincerely yours,
S. Jalali.
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Saeid Jalali Asadabadi,
Department of Physics, Faculty of Science,
University of Isfahan (UI), Hezar Gerib Avenue,
81744 Isfahan, Iran.
Phones:
Dep. of Phys. :+98-0311-793 2435
Office :+98-0311-793 2430
Fax No. :+98-0311-793 2409
E-mail :s_jalali_a at yahoo.com
www :http://www.ui.ac.ir
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Sincerely yours,
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Saeid Jalali Asadabadi,
Department of Physics, Faculty of Science,
University of Isfahan (UI), Hezar Gerib Avenue,
81744 Isfahan, Iran.
Phones:
Dep. of Phys. :+98-0311-793 2435
Office :+98-0311-793 2430
Fax No. :+98-0311-793 2409
E-mail :s_jalali_a at yahoo.com
www :http://www.ui.ac.ir
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