Second-order perturbative approximation to the SAC/SAC-CI method

The second-order perturbative approximation to the SAC (symmetry-adapted cluster)/SAC-CI (configuration interaction) method is proposed. It is used in various studies of electronic structures and spectroscopic properties of large molecules in ground, excited (singlet and triplet), ionized, and electron-attached states. The performance and the reliability of the proposed method are investigated by applications to several molecules in these electronic states.