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

[Lorenzo Paulatto]

> 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