Density-functional calculation of static and dynamic properties of GaAs

We present results of "direct" calculations of structure and lattice dynamics of GaAs using local forms of the ionic pseudopotentials and the density functional. The predicted lattice constant, bulk modulus, phonon frequencies, effective charges, and Gr\"uneisen parameters agree well with experiment. Eigenvectors at the X point are determined and used to test phenomenological models. We examine anharmonic energies and suggest a possible transition under pressure to an orthorhombic phase, related to the soft TA(X) phonon.