ATOMIC GEOMETRY AND BONDING ON THE GAAS(001)-BETA-2(2X4) SURFACE FROMAB-INITIO PSEUDOPOTENTIAL CALCULATIONS

We present detailed results of ab initio pseudopotential calculations for equilibrium atomic geometry and chemical bonding on the arsenic te rminated GaAs(001)-beta 2(2x4) surface. Of particular note is our find ing that there are two distinct Ga-As bond lengths between the first a nd second layers. This feature is due to the presence of both threefol d and fourfold coordinated Ga atoms in the second layer. Our results a dd significantly to the information available from recent first-princi ples calculations, and from scanning tunneling microscopy, reflection high-energy electron diffraction, and low-energy electron diffraction analyses.