[Pw_forum] Confusion about silicon phonon dispersion along K-X path

[Suza W]

Hi Nicola,

Thanks for SeeK-path that is extremely helpful.

Are you aware of any such code which also can provide us
phonon symmetry labels such as R_4+, M_3+ and X_5-?

QE prints such labels but hardly matches with the labels available
already in the literature.

Sincerely,
Suza


<http://materialscloud.org/tools/seekpath/>
On Sat, Jul 8, 2017 at 3:02 PM, Nicola Marzari <nicola.marzari at epfl.ch>
wrote:

>
>
> There are two gamma to X paths - the "short" one [a,0,0], where
> a goes from 0 to 1, and the "long" one [a,a,0], also with a going
> from 0 to 1.
>
> These are called the delta path and the sigma path:
> https://en.wikipedia.org/wiki/Brillouin_zone
>
> For this lattice the end points are equivalent ([1,0,0] and [1,1,0])
> but the sigma path goes though K [3/4,3/4,0]. Try to visualize in the
> wikipedia page where [1,1,0] is, and why it is equivalent to [1,0,0].
>
> Also, you can use SeeK-path
> http://materialscloud.org/tools/seekpath/
> to automatically created for any structure the k-point path that
> follows the correct crystallographic conventions.
>
>
>                                 nicola
>
>
> On 08/07/2017 07:27, balabi wrote:
> > Dear developers,
> >      I am calculating silicon phonon dispersion, however, I got confused
> > about the dispersion along K-X.
> >
> >      I found there are apparently different results on the web. Some are
> > the same with my calculation, most are not.
> >
> >      My result along k-path "Γ - K - X - Γ - L" is here:
> > https://pasteboard.co/GzWanr4.png
> >      The only result that is the same with me is on QuantumWise page :
> > http://quantumwise.com/about-us/item/836-silicon-phonon-bandstructure
> >
> >      However, most of the results that I googled is quite different
> > along K-X, for example
> > http://exciting-code.org/phonon-properties-in-diamond-structure-crystals
> >      or paper
> >      DOI: 10.1103/PhysRevB.87.165201     in which the author claimed
> > they calculate the phonon by QE
> >      I notice that the length of K-X is not the same in two different
> > result.
> >      Besides the same problem exists for similar structure like AlAs etc.
> >      But I don't know what is going wrong here? Which is the right
> > result? Thank you for helping.
> >
> > best regards
> >
> >
> >
> >
> > _______________________________________________
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> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
> >
>
>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
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