On Feb 13, 2012, at 16:41 , Lorenzo Paulatto wrote: > If you only need the phonons at the gamma point, it may be faster > to get them by finite displacement, doing 3*nat pw.x ground state > calculations.
faster? not sure, and not by much anyway. A phonon calculation at q=0 also requires 3*nat self-consistent linear-response calculations. Each such calculation has a computational cost comparable to that of a self-consistency. Usually one needs to perform two finite-difference calculations with opposite displacements in order to get good numerical accuracy, by the way. Or at least, this is the way I would do it. For q=0 phonons, using k=0 only for the Brillouiin zone sampling, and norm-conserving PP, there is the simplified version of the phonon code that is definitely faster and takes (relatively) little memory 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
