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["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Hi,

This answer might be totaly inaccurate yet:
I think that each atom in the primitive cell is related to three
phonon branches (three frequencies at each reciprocal point). Then
reducing the number of atoms may not allow you to find the complete
dynamic matrix. Yet it might be useful when your interesting only in
some part of it. For instance when someone is  working with a
structure made of thorium and hydrogen, the eigenfrequencies related
to each of these elements will probably be very different due to the
mass ratio of each of them. It may happen that one has almost not any
interest in the eigenfrequencies of hydrogen and then the keyword
"rfatpol" will help reducing the calculations. Yet now suppose that
someone is working with SiO2 the mass es of the elements are almost
the same and this keyword may be useless. Unless for some odd reasons
ones want to work with a supercell. In this case it is again usefull
to limit the response function calculations to one set of atoms.

PMA

On 8/22/06, 张�s <zhangting1980323@gmail.com> wrote:
> Dear ABINIT users:
>
>    I'm confused about the exact meaning of the keyword "rfatpol". In my
> opinion, the keyword controls which atom will be moved during the
> perturbation, in phonon calculaitons. But when I choose some atoms in the
> system(not all the atoms in the system) to be specified with this keyword,
> the code can also calculate out a set of phonon frequencies. Why just moving
> a part of atoms in a cell is OK? Is this because the symmertry of the system
> so that the code can determine the whole D-matrix with just moving some of
> the atoms in the system? And can I reduce the calculation requirement in
> phonon dispersion missions with this method? Thanks!
>    Attachments are my input and output files, in wihch there is graphite
> system, with 4 atom in a primitive cell. I used "rfatpol 3 4" in the .in
> file, and can get a set of phonon frequencies in the .out file. The accuracy
> is not important because I just want to test the meaning of the keyword
> "rfatpol"
>
>
>
>
> zhangtingPKU
> zhangting@pku.edu.cn
> 2006-08-22


--
Pierre-Matthieu Anglade