[Pw_forum] Symmetry of the dynamical matrix

[Paolo Giannozzi]

On Jul 30, 2009, at 18:47 , Cristian Degli Esposti Boschi wrote:

> using the phonon code I noticed that, even
> for simple molecular structures, the dynamical
> matrix computed by ph.x is not symmetric [...]
> In general, this does not guarantee real
> eigenvalues. How are the eigenfrequencies
> computed then?

the dynamical matrix is symmetrized before diagonalization.
There is a check that the unsymmetric part (coming from
inexact self-consistency) is small. If not, a message is issued

Paolo
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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