[Pw_forum] U calculation in LDA+U

[Peng Chen]

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




-- 
  Best Regards.
        Peng
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