[Pw_forum] phonon calculation q-grid

[Eric Abel]

I wanted to address the question dealing with q-grid density, since this is 
also an issue of interest to me.  I've been reading the literature, and 
unless I'm mistaken, the choice of q-grid density along
each principle direction is an indication of the length scale of the 
interatomic forces.  So if, for instance, one only wanted to take into 
account nearest neighbor interactions, with distance d, then the q-spacing 
along that direction would only have to be 2\pi/d, correct?  So calculating 
D at gamma, and then at q=0.5, would correspond to a force constant with a 
range spanning ~2 unit cells...or am I way off base here?

Eric