Ground- and Excited-State energies of copper oxide molecules and anions from first principles via the Spin-Flip Bethe-Salpeter Equation approach

Abstract

^*The Spin-Flip Bethe-Salpeter Equation (SF-BSE) is our new first-principles formalism to compute the electronic structure of open-shell systems, based on many-body perturbation theory. An open shell system has unpaired spins, and therefore requires methods capable of accessing multiple Slater determinants to describe its electronic properties accurately. First, the total energy and single-particle orbitals are computed with a high-spin reference state, a single Slater determinant with S = M_S. Then, a spin-flip excitation is applied to this high-spin reference state, placing an electron from an occupied up-spin orbital to an unoccupied down-spin orbital, with the electron and hole interacting through the screened Coulomb interaction. These transitions then constitute a basis set for multi-reference ground and excited states. The di- and tri-atomic copper oxide molecules and anions are examples of transition metal-containing systems with many low-lying excited