Modeling photoelectron spectra of CuO, Cu2O, and CuO2 anions with equation-of-motion coupled-cluster methods: An adventure in Fock space
The experimental photoelectron spectra of di- and triatomic copper oxide anions have been reported previously. We present an analysis of the experimental spectra of the CuO-, Cu2O-, and CuO2- anions using equation-of-motion coupled-cluster (EOM-CC) methods. The open-shell electronic structure of each cluster demands a unique combination of EOM-CC methods to achieve an accurate and balanced representation of the multi-configurational anionic and neutral state manifolds. Analysis of the Dyson orbitals associated with photodetachment from CuO- reveals the strong non-Koopmans character of the CuO states. A perturbative triples correction to the coupled-cluster singles and doubles ansatz is required for accurate description of electron detachment from Cu2O-. Use of a relativistic pseudopotential and matching basis set improves quality of results in most cases. EOM-DIP-CCSD analysis of the low-lying states of CuO2- reveals multiple singlet and triplet anionic states near the triplet ground state, adding a extra layer of complexity to the interpretation of the experimental CuO2- photoelectron spectrum.