Dear Paolo and Lorenzo, Thank you for such a detailed explanation!
Best regards, Andrei On Fri, May 17, 2013 at 3:59 AM, Paolo Giannozzi <paolo.giannozzi at uniud.it>wrote: > On Fri, 2013-05-17 at 01:18 +0800, Fang Liu wrote: > > > That is, I use a 25*25*25 3D FFT mesh. The original 3d array g3d = > > (1.0_DP, -1.0_DP). > > > > First I do invfft and then fwfft. Finally I don't get the original 3d > > array, but a 3d array g3dnew in which > > g3dnew(1),g3dnew(2),...,g3dnew(3025)= (1.0_DP, -1.0_DP) > > while g3dnew(3026),....,g3dnew(15625)=0.0. > > > But if I do fwfft first and then invfft, I can finally get the > > original 3d array. > > The 3D FFTs in QE are tailored for the "dual-space" algorithm > as used in plane-wave codes. If you specify "Wave", the code > will assume that there are no G components beyond a sphere > of radius G^2 < Ecut. For instance, when performing the G->R > FT along z, many vectors will be ignored, because they are > assumed to contain zeros. See Lorenzo's post for a more detailed > explanation. > > P. > > -- > Paolo Giannozzi, Dept. Chemistry&Physics&Environment, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130517/047fc435/attachment.html
