[QE-users] Optical branches are not continuous at gamma point in phonon dispersion

Marzari Nicola nicola.marzari at epfl.ch
Wed Nov 14 09:31:36 CET 2018

Note you can converge to different limits depending on direction, so a discontinuity in a plot where the direction changes angle is possible. Nicola

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On 14 Nov 2018, at 09:29, Lorenzo Paulatto <paulatz at gmail.com> wrote:

>> I found that optical branches are not continuous at gamma point (See figure below). I guess this is becasue the wrong LO-TO spiliting relation I got. How can I check it?
> It is definitely because of LO-TO splitting, if it is wrong or not, well you can check how it converges with k-points. Dielectric constants and effective charges can be VERY slow to converge with k-points. Just repeat the phonon calculation at Gamma, no need to redo all the grid each time.
> Or if you think the should be no LO-TO splitting at all (typically because of doping), just edit the first dyn matrix file (the one at gamma, i.e. dyn1) and remove all the section about epsilon and zeu, from
>   "Dielectric Tensor:"
> included, down to
>   "Diagonalizing the dynamical matrix"
> excluded.
> hth
> -- 
> Lorenzo Paulatto - Paris
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