quantum-espresso/examples/example34

This example illustrates how to use vdw.x to calculate 
dynamic polarizability of methane molecules (experiment stage).
The van der Waals coefficient C6 can be obtained by simply 
integrating the dynamic polarizability(not done here).
The Thomas-Fermi and von Weizsacker approximation is used
to simplify the full calculation done in ph.x. It is expected
that this simplified calculation gives results deviating
about 20% comparing to that of the full one(checked for
methane and benzene).    


The calculation proceeds as follows 

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

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