phonopy-users

[Phonopy-users] non-equivalent force constants and constraints

[Iyad AL-Q. <iy...@gm...>]

Dear Phonopy users,

Phonopy calcualted the non-equivalent set of force constants and distribute
them to those are equivalent. It applies also symmetry operations on the
force constants to conserve the clousre relations ( constraints). But all
of this is done numerically.

My question, how for a system of given number of atoms, I can extract
analytically using phonopy the list of the non-equivalent force constants
and the equations connect these force constants based on the symmetry
operations. As an example for a system of Nb using 54 atoms which means
there are 54 x 54 matrix element where each element is 3x3 matrix, that is,
there are 26244 force constants, only 16 force constants are
non-equivalent. I  did that by hand which is time consuming. If  I want to
know the relations between these force constants, please advice how.

Thank you
___________________________
IYAD I. AL-QASIR, PhD
Postdoc Research Associate

X-Ray and Neutron Scattering and Spectroscopy Group
Materials Science and Technology Division
Oak Ridge National Lab
Oak Ridge, TN

Re: [Phonopy-users] non-equivalent force constants and constraints

[Atsushi T. <atz...@gm...>]

Hi,

I don't understand what kind of technique you expect. The handling of
tensor using matrix representations of space group can be found in the
books for group theory for solids. I think the best is to read one of
those books.

By the way, phonopy does not directly apply symmetry constrains numerically.
http://phonopy.sourceforge.net/theory.html#the-palinski-li-kawazoe-method

Togo

On Wed, Mar 27, 2013 at 4:02 AM, Iyad AL-QASIR <iy...@gm...> wrote:
> Dear Phonopy users,
>
> Phonopy calcualted the non-equivalent set of force constants and distribute
> them to those are equivalent. It applies also symmetry operations on the
> force constants to conserve the clousre relations ( constraints). But all of
> this is done numerically.
>
> My question, how for a system of given number of atoms, I can extract
> analytically using phonopy the list of the non-equivalent force constants
> and the equations connect these force constants based on the symmetry
> operations. As an example for a system of Nb using 54 atoms which means
> there are 54 x 54 matrix element where each element is 3x3 matrix, that is,
> there are 26244 force constants, only 16 force constants are non-equivalent.
> I  did that by hand which is time consuming. If  I want to know the
> relations between these force constants, please advice how.
>
> Thank you
> ___________________________
> IYAD I. AL-QASIR, PhD
> Postdoc Research Associate
>
> X-Ray and Neutron Scattering and Spectroscopy Group
> Materials Science and Technology Division
> Oak Ridge National Lab
> Oak Ridge, TN
>
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-- 
Atsushi Togo
http://atztogo.github.com/
atz...@gm...