This directory shows the convergence of the phonon frequencies at X with
the k-point mesh:

dfpt222.in
dfpt444.in
dfpt666.in

The experimental values are 150 cm^-1, 410 cm^-1 and 463 cm^-1.

dfpt222.in_shift checks that the phonon frequencies are independent from
the position of the origin in the unit cell.

dfpt222.r.in checks that the phonon frequencies at the two equivalent q-points
(0.,0.,1.) and (1.,1.,0.) are equal.
