Currently the interpolation table for USPP Q functions computes q_i=Q(|G_i|) on
a grid of equally spaced |G_i| ***in units of 2\pi/a0***. As a consequence, the
number of points of the grid for a given cutoff depends upon the size of the
cell (noticed by Anton Kozhevnikov). This does not make sense: the Q functions
are atomic-like quantities and the maximum |G| depends upon the cutoff.
I moved the interpolation table from 2\pi/a0 units to atomic units, as it is
done everywhere else in QE. I am less and less convinced that storing k-points
and G-vectors in 2\pi/a0 units is a good idea, by the way.
BEWARE: this patch changes the behavior of routines init_us_1 and qvan2,
has the potential to break external codes that use QE routines.
Paolo Giannozzi