Analytically continued Fock space multireference coupled-cluster theory: Application to the [sup 2] Pi[sub g] shape resonance in e-N[sub 2] scattering

The technique of Fock space multireference coupled-cluster (FSMRCC) is applied for the first time to the correlated calculation of the energy and width of a shape resonance in an electron-molecule collision. The procedure is based upon combining a complex absorbing potential with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigenvalue problem. The potential-energy curve of the state of N2− is calculated using the FSMRCC and multireference configuration-interaction (MRCI) level of theories. Comparison with the single-determinant Hartree–Fock theory indicates that correlation effects are important in determining the behavior of the resonance state.