[Pw_forum] a question about phonon dos

[Paolo Giannozzi]

On Thursday 03 August 2006 17:41, Peter Winey wrote:

> In the description part (head) of the program, I noticed the following:
> "dos if .true. calculate phonon dos using tetrahedra and a uniform 
> q-point  grid. NB: may not work properly in noncubic materials."
>
> Could someone kindly explain to me what "using tetrahedra" means?

it means "using the tetrahedron method to perform sums over
the Brillouin Zone". See for instance:
P.E. Bloechl et al, PRB49, 16223 (1994)

> if the program does not work properly for noncubic materials, 
> how to get the proper phonon dos?

it is not that it doesn't work at all, but there will be a small
error in the contribution of the region around q=0. It is not
clear to me how to take into account the dependence of LO
phonons at q=0 upon the direction of q=>0 

Paolo
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