[Pw_forum] phonon dispersion

[Paolo Giannozzi]

On Nov 12, 2009, at 8:04 , xirainbow wrote:

> In the periodic calculation, the two rotational mode never really
> vanish due to weak interaction with the periodic images of the  
> molecule.

I think the original question was on a different subject. Even
after imposing acoustic sum rule, the frequency of translation
modes are not exactly zero. They shouldn't exceed a fraction
of a cm^{-1}, though.

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