The A4 structure has the face centered cubic Bravais lattice and two
atoms per cell. Putting one atom in the origin, the other is in 
(1/4, 1/4, 1/4) in alat units.
It is the structure of diamond.

The reference directory contains the following files:

asy_tmp.asy : asymptote script to plot the Brillouin zone

output_keconv.ps: plot of the convergence of the total energy with the
                  kinetic energy cut-off.

output_mur.ps: a plot of the energy as a function of the volume at T=0
               and a Murnaghan fit. Pressure as a function of volume.

output_bands.ps : plot of the band structure

output_disp.ps.g1 : plot of the phonon dispersion. Note that the
       experimental data are read by modifying the file gnuplot.tmp.g1_disp

output_grun.ps : plot of the mode Gruneisen parameters.

output_anhar.ps : plot of the anharmonic properties.

c.elastic.out : the output of the elastic constant calculation.
                See the end of the file for the elastic constant values.

c_ph.exp : experimental phonon frequencies

c_anharm.exp : experimental thermal expansion.
