This example illustrates how to use pw.x and ph.x to calculate 
dynamic polarizability of methane molecules (experiment stage)

The calculation proceeds as follows 

1) make a self-consistent calculation (input=ch4.scf.in,
   output=ch4.scf.out)

2) make a (imaginary) frequency dependent polarizability calculation 
   (input=ch4.fpol.in, output=ch4.fpol.out).