[Pw_forum] Different optical mode frequency at the same q-vector

Lorenzo Paulatto lorenzo.paulatto at impmc.upmc.fr
Wed Oct 10 17:13:48 CEST 2012

On 5 October 2012 00:33, dfsgdv dfsdf <dim2350 at gmail.com> wrote:

> Hi,

Dear dfsgdv dfsdf,

> I will explain my problmes with a simpe example.
> Why don't you explain posting some useful details of the actual
calculation you have done?

Assume I am doing the phonon dispersion [ ...]
> So basically my problem is that I have generated two phonon dispersion
> relation: Gamma to Z and Gamma to X, but the optical mode frequencies at
> Gamma in the two plots are different.

Either there is an error in your input, or the phonon code is smarter than
you. I.E. it is applying direction-dependent LO-TO splitting to the modes
at Gamma (one ref: <http://cmt.dur.ac.uk/sjc/thesis_prt/node62.html>)

If there is indeed a problem with your calculation, you should give us more
information in order to get meaningful help.

Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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