[Pw_forum] phonon dispersion

[Paolo Giannozzi]

On Nov 9, 2009, at 19:56 , Mehrnaz Anvari wrote:

> Although I used asr=crystal in my calculations, the acoustic
> phonons at first gamma point are not exactly zero.
> what is the reason of this happening? does it relate to
> choosing c/a in difinition of graphene?

short answers: 1) I don't know 2) no. Even after ASR is
imposed, a very small nonzero frequency (fractions of cm^{-1))
is still obtained as the rsult of the diagonalization. It might be
numrical noise in the diagonalization, though

P.
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222