  In this work, we present our theoretical results for the equation of state
and the phonon dispersions of MnAs, as well as the Mn concentration dependence
of both the lattice parameter and the phonon frequencies of the cubic GaMnAs
alloys. The results are in good agreement with the experimental results
whenever this comparison is possible. Based on the obtained results, the
lattice constants and the phonon frequencies of the alloys do not obey the
Vegard rule.
