[Pw_forum] question on random_matrix

[Paolo Giannozzi]

On Monday 22 May 2006 18:15, Virginie Trinité wrote:

> I have a question about the subroutine random_matrix in PH
> [...]  I didn't understand why if nb is never the transform of na
> by some symmetry then the dynamical matrix is zero?

the comment in the header of that subroutine reads:

  !   Create a random hermitian matrix with non zero elements
  !   similar to the dynamical matrix of the system

but this is somewhat misleading. From what I remember the 
random matrix is used to find the irreducible representations 
of the small group of q (the phonon wavevector). If no symmetry 
sends atom na into atom nb, displacements of atoms na and nb 
will belong to different irreps.

Disclaimer: I didn't write, and never really understood, how
symmetry works in the phonon code, so the above might be 
all wrong!

Paolo
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
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