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

W. YU yuwen_66 at yahoo.com
Tue Dec 19 12:30:01 CET 2006

Thanks to Stefano, Paolo and all other pw users.

Now I hope to make sure about something on phonon and
e-ph coupling calculations.

Stefano has told me a lot about consistancy while
choosing parameters for scf and nonscf. But I still
have two questions here.

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. I reached the above conclusions from example06
for AlAs where the scf and nscf calculations using 
shifted k points which comes from a 222 grid, and the
q points from a unshifted 444 grid. 

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. This
is different from a pure phonon calculation.

Please let know whether I am right or not!


Wen YU

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