Cyclic and Linear NiO2: A Multireference Configuration Interaction Study

Abstract

Linear (ONiO) and triangular (Ni(O2))isomers of NiO2 are investigated by multiconfiguration self-consistent field (MCSCF) and multireference configuration interaction (MRCI) calculations. For ONiO, the ground electronic term is a 1Σg+ term. The lower-lying excited terms are 3Πg, 1Πg, and 5Πu at relative energies of 0.55, 0.95, and 1.20eV, respectively. For Ni(O2), the ground electronic term is a1A1 term with an energy of 1.53 eV with respect to the ONiO ground state. Lower-lying excited terms are 5B2, 5A1, and 3B2 at 0.58, 0.62, and 0.73 eV with respect to the 1A1 state, respectively.A transition structure between the ground states of both isomers has been located with an energy of 2.76 eV above the ONiO ground state. For the fragmentation Ni(O2) → Ni + O2 the (electronic) reaction energy is estimated to 1.15 eV. The wave function based results demonstrate the failure of previous density functional investigations and emphasize the importance of a multireference treatment.