COVERAGE-DEPENDENT BONDING OF SB ON GAAS(110)

We performed total-energy pseudopotential calculations for a variety o f structures for Sb adsorbed on the GaAs(110) surface. Sb coverages of theta = 1 and theta = 1/2 are considered. For theta = 1 we investigat e five earlier proposed structures and find the epitaxial continued la yer structure (ECLS) to be the lowest one in energy. The epitaxial on top structure (EOTS) which fits better to recent STM images is slightl y higher in energy. The electronic structure and the changes of the io nization energies for these models are also discussed in the context o f experimental results and give further evidence for the ECLS. Its str uctural parameters are found to be in excellent agreement both with LE ED and XSW data. For a coverage of theta = 1/2 we find two equivalent minima in the total-energy surface corresponding to long-bridge positi ons in the 1 x 1 surface unit cell. Studies of 1 x 2 and 2 x 1 reconst ructions for this coverage are performed as well. Together with the en ergetical results for theta = 1 they indicate the tendency of Sb to fo rm two-dimensional clusters for low coverages as observed experimental ly.