Electronic and structural trends in small GaAs clusters

Using the Hartree-Fock method followed by second-order perturbation theory, the structural and electronic properties of the Ga_nAs_m (n + m ⪯ 8) clusters and its positive and negative ions are examined. The ground state structures are obtained through geometry optimization calculations without spatial symmetry constraints. Electronic and structural properties are then calculated. In particular it is verified an alternating behavior in the ionization potential beyond three-atom clusters. A structural pattern is noticed where the embryonic forms of these clusters are observed to present highly symmetrical configurations formed by the central As atoms. The Ga atoms appear at positions that enhance a hybridization and chemical ordering which tends 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 results is suggested.