[Pw_forum] What is the difference between Q points mesh and k points mesh

[Paolo Giannozzi]

On Jan 8, 2012, at 17:43 , Caloma Trumica wrote:

> why do we need to have such an additional setting of q points
> rather than just using k points mesh for both?

because they refer to different quantities and have different
convergence criteria. The "k-point" grid is used to perform the
integral over the Brillouin Zone; the "q-point" grid is used to
perform integrals over phonon wave vectors, or to obtain
Interatomic Force Constants in real space.

P.
---
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy

"Nothing is impossible for the man who doesn't have to do it himself"