[Pw_forum] Phonons of molecular crystal

[Guntram Schmidt]

Dear All,

I want to simulate the infrared spectrum of a molecular crystal.
As the phonon calculations usually take weeks to finish, I'd like to 
ask, wether someone of you has propositions on proper treshold values?

I'm using rpb-paw US pseudopotential (revised PBE, as suggested for 
vdW-potential) and gamma point (also said to be sufficient for molecular 
crystals).

Does the ecutrho of the preceding SCF calculation influence the speed of 
the phonon calculation?

What is a sufficient low value for the tr2_ph to get a reasonable 
(comparable to experimental values) spectrum?


Thanks a lot,
Guntram