[Pw_forum] Imaginary displacements

[Stefano Baroni]

Just to add a (hopefully, clarifying) comment.

Hermitean matrix: eignevalues are real, eigenvectors are in in  
general complex
Real symmetric matrix: eigenvalues are real (because the matrix is  
Hermitean as well). The eigenvectors *CAN* be chose to be real. This  
does not imply that they *MUST* be chosen so.

You may want to rethink to the previous replies in the light of this  
remark.
Also, I am almost certain that this very question has been already  
discussed in this forum. You may want to check the archive.

Take care
Stefano B.

On Nov 19, 2007, at 12:03 PM, Paolo Giannozzi wrote:

>
> On Nov 19, 2007, at 12:31 , Ion Errea wrote:
>
>> Does anyonone which are the reasons why you can get imaginary
>> displacements for phonon eigenmodes?
>
> at q=0 both the dynamical matrix and its eigenvectors are real,
> but for a general q, the dynamical matrix is complex hermitian
> and its eigenvectors are in general complex
>
> Paolo
> ---
> Paolo Giannozzi, Dept of Physics, University of Udine
> via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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