[Pw_forum] phonon calculaiton- shifted k points or not?
wenyu at sas.ustb.edu.cn
Wed Dec 20 05:15:18 CET 2006
Dear Paolo, thank you for your answer!
>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
>Correct: the former depends
>upon the range of interatomic force constants in real space,
>the latter upon the character of the band structure
Doesn't the above answer agree with what I said in the former post?
>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
The problem is: if you choose a shifted k-grid and a unshited q-grid, it seems
difficult to maintain the above restrictions-namely the "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
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