quantum-espresso/examples/example06

This example illustrates how to calculate interatomic force 
constants (IFC) in real space for AlAs in zincblende structure.

The calculation proceeds as follows (for the meaning of the cited input
variables see the appropriate INPUT_* file)

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

2) make a phonon calculation for a uniform grid of q-points. We chose
   a 444 Monkhorst-Pack grid, not translated. We separately calculate
   the dynamical matrix at Gamma together with effective charges 
   (AlAs is a polar system).  All dynamical matrices are saved with
   a different name.

3) call program q2r.x to calculate IFC's in real space.
   All dynamical matrices are read and Fourier-transformed. Note that
   nr1,nr2,nr3  in file q2r.in are the Monkhorst-Pack indexes of the 
   q-point uniform grid (4,4,4 in this case).
   The output file containing the force constants in a format suitable 
   for program matdyn.x is alas444.fc.

4) call program matdyn.x to recalculate phonons at any q-vector from
   previously calculated IFC's. See the header of matdyn.f90 for
   input documentation.