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

[Nicola Marzari]

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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-- 
----------------------------------------------------------------------
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