[Pw_forum] FFT on a small mesh

[dario rocca]

Dear Developers
I would be interested in calculating the FFT with a small reciprocal
space  cutoff. Namely beyond the FFT for wavefunctions
and density I would like to use an additional FFT on an "object" that
requires a cutoff smaller than the
wavefunctions (but of course the real space mesh would still be the same).
All the standard
FFT machinery seems very specialized to the
wavefunction/density case, and I was wondering if there is an easy option or
if someone
has developed more general subroutines and is willing to share them.
Thanks for your help
Dario Rocca, UCDavis
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