[Pw_forum] U calculation in LDA+U

[Burak Himmetoglu]

Hi Peng,

r.x assigns the values of the response matrices only by considering the
distance between atoms and whether they have the same spin and type or not.
This information has to be given by the user in the positions file
"filepos" read by &input_mat. If B(1) and B(2) are different types
(e.g. crystallographically) you should perturb them separately, as you
outlined in the procedure, and make sure that ntyp=3 (type 1 is B(1), type
2 is B(2) and type 3 is O) in the namelist &input_mat that goes into r.x

Best regards,

Burak

On Tue, Jul 10, 2012 at 1:45 AM, Stefano de Gironcoli <degironc at sissa.it>wrote:

>  I don't know the details of r.x code but I think that, physically, what
> matters is the two atoms are crystallographically equivalent or not
> .therefore I think space group symmetry is the relevant one.
>
> stefano
>
>
> On 07/10/2012 05:54 AM, Peng Chen wrote:
>
> Dear All,
>
> In the calculation of U, how can we determine the equivalence of the ions,
> by site symmetry or space group symmetry?
> E.g  ABO3, B ions has 2 different site symmetries (B(1) B(2)). Shall we run
> calculation on perturbing B(1) and B(2) ions or  just a B ion?
>
>  In order to find U in B  ions, I tried to run calculation with perturbing
> just on B, and r.x gave some errors that it needs to read more data.
> So I guess it needs the perturbed data from other atoms. Shall I use the
> procedures listed below?
> 1. run scf calculation with Hubbard_U(i)= 1.d-20
> 2. run scf with perturbing on an A ion
> 3.   run scf with perturbing on a B(1) ion
> 4.   run scf with perturbing on a B(2) ion
> 5.   run scf with perturbing on an O ion
>
>
>
>
>
>
>
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