AB-INITIO SELF-CONSISTENT-FIELD STUDIES OF THE STRUCTURE, ENERGETICS AND BONDING OF SMALL GALLIUM-ARSENIDE CLUSTERS

Ab initio all-electron self-consistent-field calculations are peformed on small Ga-m As-n(m+n less than or equal to 5) clusters using large basis set. The structure, energetics and bonding are analyzed for all clusters, including the positive and negative charge states. In total 18 species are utilized to give a coherent unified picture. Geometry o ptimization for all species are performed using analytic energy gradie nt. For crucial or controversial cases post-self-consistent-field calc ulations at the second-order Moller-Plesset level are performed. In sp ecial, the D-3h geometry of Ga-2 As-3 as suggested experimentally from ESR experiment is obtained only after inclusion of electron correlati on effects. We suggest an explanation to the experimentally observed m ass spectrum of clusters with a given number of atoms. The observed al ternating behavior for the ionization potentials and electron affiniti es is discussed and it is suggested that electron correlation correcti ons are important for a quantitative theoretical description.