On Sep 22, 2011, at 2:13 , dario rocca wrote: > Dear Developers
(reminder: the proper place where to contact developers is the q-e- developers mailing list on qe-forge.org) > 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 it is, by construction. In the most recent versions, however, the FFT stuff is encapsulated into a few "descriptors" that are initialized in a few specific routines. Note that the CP code has a third grid, the "small box" grid, a subset of the dense grid in real space.This is used to deal with augmentation charges in the USPP framework. You may want to have a look at it. I have heard of work done to speed up exact exchange and GW calculations, consisting in performing the needed FFT with a lower cutoff. Nothing has yet percolated to the current development version, though. P. --- Paolo Giannozzi, Dept of Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
