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

[Matteo Cococcioni]

Gianluca Giovannetti wrote:
> Dear Matteo,
>
> thank you for the link.
> now it is fine.
> i can calculate U with your scheme. :-)
>
> what about J ?
>

Dear Gianluca

the formal extension of the linear-response machinery to compute U to a 
spin-resolved case (using magnetization instead of
occupations) doesn't work to obtain J.
this is at least my experience.

regards,

Matteo
> cheers,
>
> Gianluca
>
> On Mon, Feb 15, 2010 at 2:45 AM, Matteo Cococcioni <matteo at umn.edu 
> <mailto:matteo at umn.edu>> wrote:
>
>
>     Dear Gianluca,
>
>     here is the link to a tutorial on how to compute the U:
>
>     http://media.quantum-espresso.org/santa_barbara_2009_07/index.php
>
>     This method uses the atomic occupations defined as in the PRB '05
>     paper
>     you refer to in your email.
>
>     For sure one could use Wannier functions ainstead of atomic orbitals.
>     HoweverI have no direct experience with that
>     so I cannot tell you how to do this in practice.
>
>     regards,
>
>     Matteo
>
>     Gianluca Giovannetti wrote:
>
>     > Dear All,
>     >
>     > 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.
>     >
>     > The paper "Phys. Rev. B 71, 035105 (2005)" well explains how to
>     > calculate the parameter U.
>     > i have however troubles in setting the input files to do the
>     calculations.
>     > could some examples be provided?
>     >
>     > I have also another question.
>     >
>     > 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?
>     >
>     > thank you.
>     >
>     > cheers,
>     >
>     > Gianluca
>     >
>     >
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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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