[Pw_forum] questions about lda+u calculation

[Matteo Cococcioni]

Gianluca Giovannetti wrote:
> Dear Ivanov,
>
> if you have a look to the file resp_mat.f90 you can check the reason 
> to have atomic positions read from file.
> there are needed to calculate the matrix elements of chi and chi0.
>
> atomic positions are given in fractional coordinates (direct lattice).
> what about primitive vectors?

their length is not important (as long as you maintain the symmetry of 
the actual unit cell). the code uses them
to compute distances between atoms and to recognize neighbors in the 
same shell.

>
> if you are considering a FeO unit cell with 8 ions you can perturb 
> only one Fe site (you don`t need to look at occupancies on O sites) 
> if  all the other Fe are equivalent to this one.
> one have to perturb once all the ions which are not equivalent.
>
> cheers,
>
> Gianluca
>
> 2010/2/16 Максим Иванов <maaaxim at yahoo.com <mailto:maaaxim at yahoo.com>>
>
>     Dear PW-users,
>     I have question about calculating the response matrice in lda+u
>     calculation. At the tutorial with examples at page
>     http://media.quantum-espresso.org/santa_barbara_2009_07/index.php
>     is used input file to calculate the matrice. In this input file
>     you need file containing the atomic positions and the vectors of
>     the unit cell plus number of unit cells in each direction to
>     construct the supercell. As I understand response matrice is
>     resiprocal matrix of matrix containing dn/dalfa derivatives. So,
>     why does author include atomic positions in his program?
>     In the case when there are more than two Fe atoms in FeO unit cell
>     (let's say 8) is it correct to make perturbation only for one Fe
>     atom? Or should I make perturbation for 8 Fe atoms and calculate
>     8x8 matrix?
>     Thanks in advance,
>     Maxim Ivanov
>
>     	
>
>
>
>
>
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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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