[Pw_forum] LDA+U calculations to get U and J

[Matteo Cococcioni]

Gianluca Giovannetti wrote:
> Dear All,
>
> thank you for the reply. i appreciate it.
>
> i need U and J for a DMFT (homemade) code.
> this is the reason i would prefer to calculate U and J via Wannier 
> formalism.
> Wannier functions i have calculated including d and p states/bands in 
> order to have more localized states and i can have eigenvalues for 
> self-consistent unperturbed (alpha=0) and perturbed (alpha finite) runs.
> i don`t understand if U and J calculated via derivates of eigenvalues 
> respect occupancies of this two runs are correct.
> what is your opinion?

just a little warning here: the eigenvalues are the derivatives of the 
energy with respect to the occupation of the Kohn-Sham state
they are associated with, not with respect to any occupation you may 
want to define through projection an any basis. So I suspect
that if you compute their derivative with respect to e.g. atomic or 
wannier occupations what you get is a mixed second derivative of the energy.

maybe this reference will be useful too for you to use pwscf to compute 
U on a basis of WF:

J. Phys. Chem. B 2005, 109, 22860-22867

regards,

Matteo
>
> i have the feeling that i should take care to extrapolate for 
> different sizes of my system in what i`m doing.
>
> What do you mean by  "very similar but another procedure"?
>
> thank you.
>
> Gianluca
>
>
>
> On Mon, Feb 15, 2010 at 10:10 AM, Dmitry Korotin <dmitry at korotin.name 
> <mailto:dmitry at korotin.name>> wrote:
>
>     Dear Gianluca,
>
>     > i would like to calculate the U and J for a given material Fe based.
>     > I can do LDA+U calculations without problems is such system
>     using PW.
>
>     If you are going to use U and J within original QE code you should
>     calculate U and J for atomic states as Matteo Cococcioni suggests.
>
>     > In the current distribution of PW in the directory PP there is a
>     file
>     > wannier_ham.f90.
>     > I believe it is referring to the paper:
>     >
>     > http://xxx.lanl.gov/pdf/0801.3500
>     >
>     > The subroutines are reading wfs and eigenvalues of a given
>     self-consistent
>     > calculation and they calculate the Hamiltonian in Wannier basis set.
>     > This gives the possibility to calculate on-site energy of given
>     d states.
>     > If now we change the occupancy at a given site by the flag
>     Hubbard_alpha()
>     > and we recalculate the Hamiltonian in Wannier basis set for such
>     > self-consistent calculation, the variation of eigenvalues
>     respect to the
>     > occupations should give the U and J parameters.
>     > Is this correct?
>     > Is this the procedure used in the mentioned paper?
>
>     In the mentioned paper was used very similar but another procedure.
>     With use of the flag Hubbard_alpha() you are able to change occupancy
>     of a pure atomic (pseudoatomic) orbital. If Wannier function differs
>     noticeably from pure atomic state standart procedure is not suitable.
>
>     --
>     Best regards,
>     Dmitry Korotin
>
>     Ph. D. Student,
>     Institute of Metal Physics
>     S. Kovalevskaya, 18
>     620041 Ekaterinburg GSP-170
>     Russia
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>
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-- 
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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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