Many-body Green's-function method for electron scattering from open-shell systems

It is shown how the many-body Green's-function method, previously developed by the authors for treating elastic and inelastic electron scattering of closed-shell systems, can be extended to open-shell systems. The method can now be applied to all open-shell systems where at least one of the members (generally those of highest and lowest multiplicity) of the degenerate multiplet can be adiabatically connected to a single-determinant unperturbed state. The resulting S-matrix is the sum over partial-wave S-matrix elements for the highest (or lowest) multiplicity state: all of which elements can be calculated by the standard many-body Green's-function techniques, which have been developed for closed-shell systems: weighted with the appropriate transformation matrix elements and Clebsch-Gordan coefficients