Calculation of dynamic polarizabilities with a multideterminental ket including a dipole-moment factor: Extrapolation method and application toLi2, LiH, and CO

An alternative method is proposed for the calculation of dynamic polarizability: one that combines the usual development over the excited states with additional terms obtained by multiplying the zeroth-order wave function with a dipole-moment factor (i.e., a polynomial of first degree in the electronic coordinates). The zeroth-order wave function includes correlation effects accounted for by a configuration-interaction perturbation subspace iterative method. The dipole-moment factor makes extrapolation possible if the number of states is limited. Applications are presented for ${\mathrm{Li}}_2$, LiH, and CO. The obtained values are in excellent agreement with the experimental ones. The analysis of the calculations shows that the extrapolation is not necessary for ${\mathrm{Li}}_2$ and LiH, the first excited states of which are of valence character, contributing strongly to the polarizability. In the case of the parallel component of the polarizability of CO, extrapolation is necessary because the first excited state of valence character appears in the seventh ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ state. In addition, we have calculated transition energies and moments for the few low-lying excited states of ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }$ symmetry for each molecule.