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["Resul Eryigit" <resul@ibu.edu.tr>]

----- Original Message ----- 
From: "Marcel Mohr" <marcel@physik.tu-berlin.de>
To: <forum@abinit.org>
Sent: Monday, May 07, 2007 4:06 PM
Subject: [abinit-forum] Wurtzite phonon disp./ discontinuity in Gamma-A 
direction


> Dear abiniteros
>
> the calculated phonon dispersion of GaN shows some kind of discontinuity
> in the Gamma-A direction for 2 optical modes.
> The section is plotted here: (and in the attachment)
> http://www.physik.tu-berlin.de/~marcel/tmp/disp_1.jpg
>
> Evreything else looks fine, but these 2 differ by approx 4 cm^-1.
>
> Any hints would be appreciated. (also keywords to search for)

dear marcel,
probably its because of the anisotropy of the wurtzite structure. on 
symmetry grounds, nonanalytic contribution to dynamical matrix (i. e. born 
effective charge and dielectric tensors)  would be anisotropic, and
lo-to splitting of phonons with q along z-direction (\Gamma-A) would be 
different than that of the ones with q along x or y (\Gamma-M).
you can do a single \Gamma point calc. and check it with anaddb keyword 
"qph2l" along z and y.

regards
resul


> Best regards
>
> Marcel Mohr