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
