[Pw_forum] atoms displacements and symmetry

[yumin qian]

      Dear Prof.
         I did a phonon calculation for a p4/nmm  crystal at Gamma point
but when I  look at the output
    file there appares several representation and  blocks  data of phonon
polarization

     Atomic displacements:
     There are  16 irreducible representations

     Representation     1      2 modes - To be done
     Phonon polarizations are as follows:
                           mode #   1                           mode #   2
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (  -0.70711   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (  -0.70711   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.70711   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.70711   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000   )
           (   0.00000   0.00000   )            (   0.00000   0.00000


    I wander how the atoms in the unit cell are displaced, for a real
calculation
  what's the relation between polariztion vector and atoms displacements
    and the relation between phonon mode , how to use the symmetry group to
    get the phonon polarization and atoms displacements pattern ,  if the
crystal have inversion symmetry ,
   so is it correct to say a particular phonon mode have or not have
inversion symmetry.
     Can anyone anwser my question , I will be very gratefull .--

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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