  The alchemical mixing approximation which is the ab initio pseudopotential
specific implementation of the virtual crystal approximation (VCA), offered in
the ABINIT package, has been employed to study the wurtzite (WZ) and zinc
blende (ZB) InxGa(1-x)N alloy from first principles. The investigations were
focused on structural properties (the equilibrium geometries), elastic
properties (elastic constants and their pressure derivatives), and on the
band-gap. Owing to the ABINIT functionality of calculating the
Hellmann-Feynmann stresses, the elastic constants have been evaluated directly
from the strain-stress relation. Values of all the quantities calculated for
parent InN and GaN have been compared with the literature data and then
evaluated as functions of composition x on a dense, 0.05 step, grid. Some
results have been obtained which, to authors' knowledge, have not yet been
reported in the literature, like composition dependent elastic constants in ZB
structures or composition dependent pressure derivatives of elastic constants.
The band-gap has been calculated within the MBJLDA approximation. Additionally,
the band-gaps for pure $InN$ and GaN have been calculated with the Wien2k code,
for comparison purposes. The evaluated quantities have been compared with the
available literature reporting supercell-based ab initio calculations and on
that basis conclusions concerning the performance of the alchemical mixing
approach have been drawn. ...
