Exponentially generated configuration interaction (EGCI) method applied to high‐spin multiplicity

The exponentially generated configuration interaction (EGCI) method is extended to high‐spin multiplicity. This method, in which excited, ionized, and electron attached states are calculated on the basis of the correlated wave function of the ground state, is applicable to quasidegenerate states of various spin multiplicity and various number of excitation processes. The accuracy and efficiency of the EGCI method is examined for the high‐spin quasidegenerate states with multiple excitation nature. Test calculations are performed for several high‐spin states of C₂, C₂⁺, N₂, N₂⁺, and m‐phenylenebis(methylene) (m‐PBM) molecules. The EGCI method reproduces well the full‐CI results in total energy, spectroscopic constants, and spin density distributions. The EGCI method is confirmed to be accurate and useful not only for investigating the energetics involved in the study of dynamics and reactions but also for studying spin density distributions of various spin multiplet states.