[Pw_forum] question about q-point and eigenvector from ph.x

[Stefano de Gironcoli]

In general eigenmodes are neither transverse nor longitudinal.
Only when the symmetry of the small group of q is sufficiently high
eigenmodes can be labeled as T or L.
stefano

On Tue, 21 Feb 2006, Konzern wrote:

> Dear all,
>
> There is one question always puzzles me. If my understanding is correct,
> for lattice dynamics, the q-point denotes the propagation direction of the
> lattice wave, while the eigenvector represents the vibration direction of
> a specific atom. Waves whose eigenvectors are perpendicular to the
> q-point are transverse waves while parallel are longitudial wave. Moreover,
> there should be 2N transverse modes and N longitudial ones.
>
> However, I checked the results from ph.x, there did not seem to exist
> such relations. I am afraid if my understanding was wrong or I have used
> the wrong interpretation of the eigenvectors.
>
> Anyone can help me out?
>
> Besides, the eigenvectors given by ph.x should be in cartesian coordination,
> right?
>
> Thanks.
>
> Konzern
>