Exponentially generated configuration interaction theory. Descriptions of excited, ionized, and electron attached states

A method of calculating wave functions of excited, ionized, and electron attached states on the basis of the correlated wave function for the ground state is given. This method, called excitator method, is a generalization of the SAC-CI (symmetry adapted cluster–configuration interaction) method. The excitator method is applied to the exponentially generated configuration interaction (EGCI) method previously proposed. The computational algorithm is described and test applications are performed for several lower states of the singlet, triplet, ionized, and anion states of CO and C2 at different internuclear distances. The accuracy of the proposed EGCI method is shown to be good relative to the full-CI energies for various states with different multiplicities, different numbers of electrons, different single and multi-electron processes, and different internuclear distances. Although the sizes of the present test calculations are small, these properties are important for studying dynamics and reactions involving different electronic states.