[Pw_forum] IFC's

[Nicola Marzari]

Ezad Shojaee wrote:
> i want to know that are we able to use the 'IFC's calculated with two 
> grids' together? for example we calculate them by a 3*3*3 grid, and then 
> 4*4*4 , then use all of them in calculating C(q) for an arbitrary point 
> in the Brillouin zone?


Dear Ezad,


with the phonon code you calculate the dynamical matrix at any
arbitary q. Usually a regular nxnxnx grid of q is chosen, you fourier 
transform it in real space to get a nxnxn set of IFCs, and you fourier
back at any arbitrary q. It's called Fourier interpolation. Details
(important, for polar materials) are in the original Giannozzi 1991 PRB,
and in the recent Baroni Rev Mod Phys (2004, I believE).

Also, do not forget your affiliation in the emails.

			nicola

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