Non-compact structures and magnetic behavior of rhodium clusters

Small clusters of rhodium having 2 to 15 atoms have been studied using the ab initio ultrasoft pseudopotential method and the generalized gradient approximation for the exchange-correlation energy in order to explore the atomic structures and the evolution of magnetism. Our studies show that rhodium clusters do not prefer icosahedral growth but more open cage-like structures. For Rh₁₃ open structures are amongst the lowest energy isomers with about 1 m_B/atom magnetic moment. These are ferromagnetic in contrast to the non-magnetic bulk. Interaction with a hydrogen atom leads to a higher energy isomer to become lowest in energy with its magnetic moment reduced from 11 to 6 m_B. Rh₁₅ is the first cluster with an atom at the center. Our results agree with the available experimental data on magnetic moments.