[Pw_forum] LDA+U

[Matteo Cococcioni]

Dear Ali,

your email is confusing so I don't know if I will be able to answer.

calculations of U on isolated atoms are problematic (why do you want to 
do that?) because the system has a discrete set of
energy levels and so linear response based on the continuum variation of 
on-site occupations have little meaning. Also there is no
way the electrons can move on other energy levels when you perturb 
entire l multiplets unless the pertubation is of the same order
of the energy difference.

yes if you compute the U in the bulk (a supercell is a bulk calculation) 
you obtain a different value. you actually need to
study the convergence of U with the size of the supercell used in its 
calculation.

hope this helps.

regards,

Matteo



ali kazempour wrote:
> Dear all
> My results after doing LDA+U is very strange for isolated Ti atoms. 
> For d(alpha)/d(n) I see discontinuities .is our result true? And is 
> any way to correct that?
> Another question:If our calculation for U instead in the bulk,  would 
> be done in big supercell, Do I get different value for U or both are same?
> thanks  a lot
>
> Ali Kazempour
> Physics department, Isfahan University of Technology
> 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
> Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>
>
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Matteo Cococcioni
Department of Chemical Engineering and Materials Science,
University of Minnesota
421 Washington Av. SE
Minneapolis, MN 55455
Tel. +1 612 624 9056    Fax +1 612 626 7246
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