Outer- and inner-valence ionization spectra of N2 and CO:: SAC-CI (general-R) compared with full-CI spectra

The SAC-CI (symmetry-adapted-cluster configuration-interaction) (general-R) method describes the ionization and shake-up spectra of N2 and CO in almost complete agreement with the full-CI results, though the computational labour of the former is much smaller that that of the latter. The SAC-CI (general-R) method is accurate for both valence and inner-valence regions of ionization spectra, while the SAC-CI (SD-R) method is good for the outer-valence region, but not always so for the shake-up region.