[Pw_forum] U calculation in LDA+U

[Peng Chen]

Thanks Dr. Matteo. That is helpful.

On Tue, Jul 10, 2012 at 11:15 AM, Matteo Cococcioni <matteo at umn.edu> wrote:

> Dear Peng,
>
> let me add one word to Burak's.
> you need to distinguish two O kinds anyway, whether you shift the
> atomic position or not. if you don't do that you will be perturbing
> all the oxygen atoms at the same time.
> The necessity to have the perturbed atom described as of a different
> type (although with the same pseudopotential) is what makes it
> convenient (most of the time) to place it at the origin of the unit
> cell.
>
> best,
>
> Matteo
>
>
>
> On Tue, Jul 10, 2012 at 10:03 AM, Peng Chen <pchen at ion.chem.utk.edu>
> wrote:
> > When O is perturbed in the case of NiO in tutorial, it
> is re-positioned and
> > there are 2 different kinds of O (first with 1 atom, the second with 7
> > atoms).  Then the kind with only one O is perturbed. In the tutorial, it
> > reads "This is done to preserve the largest possible number of
> symmetries".
> >  Is this process necessary? Can we just run computation without
> re-position?
> > In that case, there is only one kind of O with 8 atoms.
> >
> > In the position file "filepos", the scale of cell length is always 10,
> even
> > if the scale is 7.9 in NiO and 5.42 in Fe. Shall we always use 10 in
> > position file no matter what the real scale is?
> >
> > On Tue, Jul 10, 2012 at 9:37 AM, Burak Himmetoglu <himm0013 at umn.edu>
> wrote:
> >>
> >> 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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> >>>
> >>>
> >>>
> >>>
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> >>
> >>
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> >
> >
> >
> > --
> >   Best Regards.
> >         Peng
> >
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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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-- 
  Best Regards.
        Peng
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