Dipole polarizabilities and hyperpolarizabilities of the small conjugated systems in the π-electron coupled cluster theory

In this work, π-electron dipole polarizabilities and hyperpolarizabilities of some organic systems with double and triple bonds (polyenes, polyynes, and condensed hydrocarbons) have been calculated using the coupled-cluster (CC) π-electron method. It is shown that the CC approach gives the polarizabilities and hyperpolarizabilities which are considerably closer to the full configuration interaction (FCI) results than the results of the Hartree-Fock method and the second order perturbation theory. A correct description of (hyper)polarizabilities of polyenes can be achieved at the CC level of theory with the inclusion of only single and double electron excitations from the Hartree-Fock determinant (the CCSD approach). However, for systems with triple bonds (acetylenes), higher level excitations need to be explicitly included in the calculations to correctly describe their (hyper)polarizabilities.