OK, I see, it is the acoustic phonon that gets imaginary. Then you are right, it is an accuracy issue, but it can be fixed by imposing the Acoustic Sum Rule in the dynmat.x or matdyn.x run (see PHonon/example02, for instance). Otherwise you would have to raise cutoffs and number of k-points to very high values in order to get a decent frequency.
Gabriele On 08/20/2014 11:13 AM, Kvasov Alexander wrote: > Dear Gabriele, > yes, I changed the volume, it's less then the relaxed value. this way > TO phonon is stable at gamma point. > the right values for TA branch should go to 0. > Alexander -- Dr. Gabriele Sclauzero ETH Zurich Materials Theory HIT G 43.2 Wolfgang-Pauli-Str. 27 8093 Z?rich, Switzerland Phone +41 44 633 94 10 Fax +41 44 633 14 59 gabriele.sclauzero at mat.ethz.ch http://www.theory.mat.ethz.ch/people/postdocs/gsclauze -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140820/cbdf88d1/attachment.html
