## phonopy-users

 [Phonopy-users] non-equivalent force constants and constraints From: Iyad AL-QASIR - 2013-03-26 19:02:17 Attachments: Message as HTML ```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 From: Atsushi Togo - 2013-03-26 22:57:47 ```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 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 > > ------------------------------------------------------------------------------ > Own the Future-Intel® Level Up Game Demo Contest 2013 > Rise to greatness in Intel's independent game demo contest. > Compete for recognition, cash, and the chance to get your game > on Steam. \$5K grand prize plus 10 genre and skill prizes. > Submit your demo by 6/6/13. http://p.sf.net/sfu/intel_levelupd2d > _______________________________________________ > Phonopy-users mailing list > Phonopy-users@... > https://lists.sourceforge.net/lists/listinfo/phonopy-users > -- Atsushi Togo http://atztogo.github.com/ atz.togo@... ```