ELECTRONIC AND STRUCTURAL TRENDS IN SMALL GAAS CLUSTERS

Using the Hartree-Fock method followed by second-order perturbation th eory, the structural and electronic properties of the GanAsm (n + m le ss than or equal to 8) clusters and its positive and negative ions are examined. The ground state structures are obtained through geometry o ptimization calculations without spatial symmetry constraints. Electro nic and structural properties are then calculated. In particular it is verified an alternating behavior in the ionization potential beyond t hree-atom clusters. A structural pattern is noticed where the embryoni c forms of these clusters are observed to present highly symmetrical c onfigurations formed by the central As atoms. The Ga atoms appear at p ositions that enhance a hybridization and chemical ordering which tend s to that presented by the bulk. The change for a layer-type structure is observed to occur already in the eight-atom stoichiometric cluster . A theoretical explanation of previously obtained mass spectrometry r esults is suggested. (C) 1998 Acta Metallurgica Inc.