Geometry and electronic structures of magic transition-metal oxide clusters M₉O₆ (M = Fe, Co, and Ni)

The magic oxide clusters M₉O₆ (M = Fe, Co, Ni) are found by using reactive laser vaporized cluster source. From the first-principles calculations, the possible equilibrium geometries for these three oxide clusters are determined to be a C_2v symmetry, where the skeleton composed of 9 metal atoms also has C_2v symmetry, different from the equilibrium structures of pure transition metal cluster M₉. The O atoms are energetically more favorable to cap the triangle surfaces. In Fe₉O₆ and Co₉O₆ clusters, oxygen atoms are antiferromagnetically polarized while ferromagnetically polarized in the Ni₉O₆ cluster, similar to the case of O atoms adsorbed on the reconstructed Ni(110) surface. The magnetic behaviors are explained from electronic structures.