On Jun 19, 2011, at 10:44 , xu yuehua wrote: > my results of example 15 has a liittle difference in alas.ph.out. > i think it can not be neglected??
the difference between "true" frequencies is very small. The non-zero value for the acoustic frequency is a well-known and hard to solve problem. Those number vary a lot from machine to machine and from version to version, but as long as they are small and disappear by applying the Acoustic Sum Rule, they are not a problem 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
