Study of energetics of end‐on and side‐on peroxide coordination in ligated Cu2O2 models with State‐Specific Equation of Motion Coupled Cluster Method

Abstract

AbstractNewly developed State‐Specific Equation of Motion Coupled Cluster method (SS‐EOMCC) is used to study the relative energetics of μ‐1:2(trans end‐on) and μ‐η2:η2(side‐on) peroxo isomers of Cu2O2 fragments with 0 and 2 ammonia ligands. These model systems had been shown to be problematic to multireference perturbation theory (MRPT) and density functional theory (DFT) methods. In spite of the small reference space used, SS‐EOMCC gives much improved results by comparison to benchmark CR‐CC results. In addition to the fully symmetric 1Ag state, 1Bg and 3Bg states are also computed, demonstrating the complexity of the systems under study, as seen from the energy crossing at intermediate geometries. Spin‐flip idea is natural in our current theoretical framework and is tried for the model systems. It is argued that an important feature of the SS‐EOMCC method is that orbitals are optimized in the presence of dynamical correlation. This is the prime reason that a very small set of active orbitals can be used to achieve satisfactory results. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008