# [Pw_forum] Phonon DOS per polarization

Bo Qiu 200210qb at gmail.com
Fri Oct 26 07:55:19 CEST 2012

```Dear Dr. Paulatto,

Thanks a lot for the explanations! I'm actually writing a small code to
order phonon bands based on eigenvector continuities on a 3d grid. Thanks
for pointing out there is already such option in matdyn.x, I'll definitely
check it out. I have finished a preliminary test for my code on Al for a
band crossing along Gamma-K direction -- it seems to be well captured,
but band orderings are wrong at some random point where there is actually
no band crossing. I'll try to figure it out and also referring to the
matdyn.f90 to see what else I can do.
On the other hand, I think for electronic band structures one will have the
same problem with band ordering -- though most of time people are only
interested about those very few bands near Fermi level. I wonder in the
case of electronic band structure whether continuity of wavefunction should
be used to deal with band ordering with band crossing? Thanks a lot!

Bo

On Thu, Oct 25, 2012 at 5:05 PM, Lorenzo Paulatto <
lorenzo.paulatto at impmc.upmc.fr> wrote:

> Dear Bo,
> as long as you can properly characterize the band, it is not hard to do:
> you can use matdyn.x to compute the phonon in a dense grid of q-points, you
> can generate it with pw.x or with the kpoint.x utility. Then load the grid
> in matlab or octave or similar and integrate it properly. Since some time
> ago, the matdyn code produce a *.gp code which is very practical for this
> kind of analysis.
>
> The problem is deciding which is band X, as soon as they start to cross
> deciding which is which is not trivial. There is an option in matdyn to
> assign the phonon bands order using eigenvectors continuity. However, this
> method works well for high-symmetry lines, but may be not so robust when
> doing a 3D grid of points. Yet, it is worth trying.
>
> Provided all these difficulties, in many case and as long as you are
> interested in a phonon band that is well separated from  the others there
> may be no problem at all. Finally, you can think of a specific criteria to
> discriminate the bands in a specific material, but implementing it is up to
> you.
>
> bests
>
> --
> 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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