On Aug 20, 2009, at 16:01 , Marcello Rosini wrote: > 4. Is it true for pw.x V(G=0)=0? no. Please have a look at this: www.fisica.uniud.it/~giannozz/public/plane_waves.pdf P. --- Paolo Giannozzi, Dept of Physics, University of Udine via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222