Generalized overlap amplitudes using the extended Koopmans’ theorem for Be Available to Purchase

Approximate generalized overlap amplitudes (GOAs), also called Feynman–Dyson amplitudes, have been calculated from a full configuration interaction (CI) wave function for the ground state of beryllium using the extended Koopmans’ theorem (EKT). The GOAs were also calculated from the ground state CI wave function for Be and the ground state and excited state CI wave functions for Be⁺. The EKT GOAs are nearly identical to the corresponding CI GOAs for the lower ²S states of Be⁺ and for the Be⁺ 1s2s² state which has a large GOA occupation number. There are many CI GOAs for which there is not a corresponding EKT GOA. This may be due in part to the limited size of the basis set and to the inability to include natural spin orbitals with small occupation numbers in the EKT calculations.