[Pw_forum] Imaginary displacements

[Stefano de Gironcoli]

check your algebra text-book. 
An hermitian matrix has real eigenvalues and in general complex 
eigenvectors.
If you are surprised think of simple example where you KNOW the answer...
For instance free electrons: the hamiltonian is real, the eigenvalues 
are real...
the eigenvectors are plane-waves (i.e. complex funcions)
Stefano de Gironcoli

Ion Errea wrote:
> Dear all,
>
> Does anyonone which are the reasons why you can get imaginary
> displacements for phonon eigenmodes? As far as I remember from algebra,
> the dynamical matrix is real and symmetric, thus hermitian, and
> hermitian matrices have real eigenvectors and eigenvalues. Therefore I
> don understand why I get this results. Problems with convergence maybe?
>
> Thanks for your answers,
>
> Ion
>
> ====================================================================
> Ion Errea Lope
> Department of Condensed Matter, Unibersity of the Basque Country
> Apdo. 644
> 48080 Bilbao (Spain)
> Tlf: +34 94 601 5322
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