[DFTB-Plus-User] Phonon dispersion using single k-point hessian calculations.

[Bálint Aradi]

Dear Anshu,

> I am wondering if it is possible to calculate phonon dispersion for a
> periodic structure by calculating hessian matrix (and corresponding
> frequencies using 'modes') at various k-points (single k-point at a
> time)? If we use "supercellFolding" to define k-points for the
> calculation of hessian matrix, is this a k-point average hessian matrix
> or just one point (k=0) hessian matrix?

If you use 'modes' to calculate the Hessian, you will get the Hessian
for the q=0 (not k!) phonon of the given system. The specified k-points
in the calculation only determine the quality of the Hessian (better
averaging over the BZ for the *electronic* part results in more accurate
forces and more accurate Hessian). But it will be still the q=0 phonon,
as atoms in the periodic images will be displaced the same way, as those
in the central cell.

You may be interested, the with the help of phonopy, you can calculate
proper phonon band structures with DFTB+:

https://atztogo.github.io/phonopy/dftb+.html


Best regards,

Bálint



-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/


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