[Wien] total energies of different spin states with LDA+U

[Peter Blaha]

I would agree that different spin-states can be compared for fixed U.
However, different spin states could (or should) have different
"U" values (maybe they differ only by a few tenth of an eV, but this is enough
to give the "wrong" spin state).

So in my opinion one can use LDA+U to find the lowest configuration, but
there is no guarantee that it is the "correct" solution. We know cases where 
it seems to work, but others don't.
 

> I don't remember whether I was involved in the discussion you mention,
> but anyway:
> 
> For some time, I was convinced about the statement that total energies
> with LDA+U did not have the same meaning as total energies with LDA,
> because the ad hoc insertion of 'U' breaks the variational procedure
> that gives the total energy its meaning. However, someone pointed me to
> a paper (from H. Eschrig, I don't have the reference at hand) where it
> was shown that *for fixed U* there is a normal variational procedure at
> work. That would mean that total energies for fixed U can be compared,
> regardless how different the spin states are.
> 
> If somebody has similar or different opinions on this topic, I am
> interested to hear them.
> 
> Stefaan
> 
> 
> > Dear Wien2k users and developers,
> > 
> > I remember a discussion in the mailing-list where some users claimed
> > that it was
> > not possible to compare total energies within LDA+U for the case of
> > very
> > different spin states (and correspondingly very different density
> > matrices), but
> > I couldn't find it on the archives. I don't remember the reasoning
> > that person
> > followed nor who it was. Does anybody have an idea on this?, is that
> > reasoning
> > right or is it really possible to compare total energies for very
> > different spin
> > states?. Does anybody know any reference where this is discussed?.
> > 
> > Thank you for your opinions,
> > 
> > -- 
> > Victor Pardo (PhD Student)
> > Electromagnetism - Applied Physics Department
> > University Santiago de Compostela
> > Facultad de Fisica, Campus Sur s/n, E-15782 Santiago de Compostela
> > (Spain)
> > Phone: +34 981 563100 Ext:13960     email: vpardo at usc.es
> > _______________________________________________
> > Wien mailing list
> > Wien at zeus.theochem.tuwien.ac.at
> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> > 
> > 
> 
> 
> -- 
> Stefaan Cottenier
> Instituut voor Kern- en Stralingsfysica
> K.U.Leuven
> Celestijnenlaan 200 D
> B-3001 Leuven (Belgium)
> 
> tel: + 32 16 32 71 45
> fax: + 32 16 32 79 85
> e-mail: stefaan.cottenier at fys.kuleuven.ac.be
> 
> 
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> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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