[Pw_forum] phonon calculaiton- shifted k points or not?

[Paolo Giannozzi]

On Dec 19, 2006, at 12:30 , W. YU wrote:

> First for phonon calculation: it seems we can use both
> shifted and unshifted k points for scf and nscf(phonon),
> but unshifted q points for phonon. The q point grid is not
> necessarily a factor of k point grid.

you mean: "the choice of the q-point grid (i.e. the grid used
to calculate the interatomic force constants) does not depend
upon the k-point grid (i.e. the grid used to perform the
self-consistent calculation")? Correct: the former depends
upon the range of interatomic force constants in real space,
the latter upon the character of the band structure

> Second, for e-ph coupling. it seems we must use all
> unshifted k points and the from the readme of
> example07, the dense grid must contain all k and k+q
> grid points used in subsequent e-ph calculation.

I am not sure that the grid used in the scf calculation
must be unshifted. What is sure is that the "dense grid"
must contain all k-points used in the scf calculation and
all the k+q points, where q are the phonon wavevector
at which the electron-phonon coefficients are calculated

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy