[Pw_forum] fft 3D

[Paolo Giannozzi]

On Fri, 2013-05-17 at 11:46 +0200, Gabriele Sclauzero wrote:
>  
> >> In real space, the wavefunction is a real vector.
> >> only for k=0 or if there is inversion symmetry
> 
> Isn't it enough to have time reversal symmetry?

time-reversal symmetry guarantees that \psi^*_{-k}=\psi_{k},
IIRC, so it guarantees that wavefunctions are real at k=0.
At a general k, wavefunctions are obviously complex,
but in presence of inversion symmetry one can always 
write them as a purely real or purely imaginary function
times the Bloch factor. This is however not currently
used in QE.

P.
-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222