
These examples illustrate how to use pw.x and ph.x to calculate 
phonon frequencies at Gamma and K for graphite using 
 DFT+D2 (Grimme), vdW-DF, vdW-DF2 and rVV10

The number of k points and cutoff are set to very small
values in order to have a fast testing case to compare with.
Much denser k-point grids and higher cutoff values are needed 
in order to obtain converged results.

As for the xc functional that should be used in combination with 
vdW xc functionals (set to pbe in the example in order not to 
upload too many pseudopotentials) it actually is as follows:
rw86 for rVV10, rw86 for vdw-df2, revpbe for vdw-df



