[Pw_forum] Phonon DOS in noncubic materials

[Rajendra Prasad fc phy]

Dear Profs. Baroni and Giannozzi,

Thank you for your prompt response and the clarification.

R. Prasad
IIT Kanpur


On Fri, 23 May 2008, Stefano Baroni wrote:

> I think (others may want to confirm or deny) that this depends of the
> non-analytic behavior of the dynamical matrix in the long-wavelength
> limit. Because of this, phonon frequencies at q=0 are strictly
> speaking not defined. Their limit as q->0 is indeed well defined only
> once the direction of q and of the phonon polarization is specified.
> For cubic materials, this non-analiticity gives rise to the well known
> LO-TO splitting, whereas for crystals of lower symmetry the situation
> is more complicated. If the DOS is calculated using a very fine mesh
> of q points, I would expect that the result would be independent on
> what happens around q=0. If, instead, too few points are used, I would
> not be surprised if the above-mentioned non-analytic behavior would
> severly undermine the accuracy of any sensible interpolation procedure
> needed for any integration (such as the one used for DOS
> calculations). Hope this is not too wrong, and of some help as well. SB
>
> On May 23, 2008, at 7:25 AM, rprasad at iitk.ac.in wrote:
>
> > Dear PWSCF users and developer,
> >
> > There is a comment in matdyn.f90 that it may not work for noncubic
> > materials for calculating phonon DOS. Why is so? Is there a simple
> > way to
> > modify the program for noncubic materials?
> >
> > R. Prasad
> > IIT Kanpur
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>
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -
> Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
>
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