[Pw_forum] phonon dispersion with experimental structure

[ding]

Dear everyone,
  Does one have to relax the structure before doing phonon calculations?  If I calculate the phonon dispersion of a material with the experimental structure at different pressures, Can I get get the phonon dispersions without negtive frequencies at different pressures ? I know that one has to optimize the structure before doing phonon calculation when using the small displacement method, but I am not sure if one has to optimize the structure before doing phonon calculations when using linear response  theory. I want to calculate  the electron-phonon interaction properties with the experimental structures at different pressures. If I don't optimize the structures, Can I get the phonon dispersions without negtive frequencies ?
Thanks in advance!
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20130501/7940226a/attachment.html>