[Pw_forum] Regarding LA_TA modes

Lorenzo Paulatto lorenzo.paulatto at impmc.upmc.fr
Wed Jul 30 15:56:58 CEST 2014


On 07/30/2014 03:20 PM, Kondaiah Samudrala wrote:
> Dear all,
>
> I'm wondering if anybody knows how to identified LA-TA modes along high symmetry directions.
>

If the displacement pattern of the atoms and the q-point are parallel, 
the mode is longitudinal; if they are orthogonal the mode is transverse. 
When a special q point has a symmetry equivalent copy that is orthogonal 
to itself, TA and LA will be degenerate, I'm not sure this is the only 
case when this can happen.

bests

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
+33 (0)1 44 275 084 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/
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