[Pw_forum] phonon symmetry and mode

[yumin qian]

One thing that confuse me is the irreducible BZ k-points in
phonon calculation.
   We use a q-points mesh in order to get the interatomic force constant.
      becuase of crystal symmetry we need not to calcaculate all the q
points but a minimum of irreducible q-points.
     And in non-selfconsistent calculation of electron structure with fixed
charge  for a give q point . why we should use the symmetry of samll group
of S(q) ? The group of S(q) is a subgroup of crystall lattice symmetry group
S(L) ,what it the difference between these two symmetry group, how to
determine S(q) from S(L)? so is this subgroup of S(q) determines the phonon
mode at point q  ?



-- 
Sincerely Y. M. Qian
Lab.of Condensed Matter Theory and Materials Computation
Institute of Physics
Chinese Academy of Sciences
Tel:  + 8610 8264 9147
E-Mail:yuminqian at gmail.com <E-Mail%3Ayuminqian at gmail.com>
P.O.Box 603   Beijing 100190
China
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