Molecular nonlinear optical parameters of π-conjugated nonalternant hydrocarbons obtained in semiempirical local coupled-cluster theory

The π-electron dipole polarizabilities and hyperpolarizabilities of organic conjugated hydrocarbons with odd-membered carbon cycles (nonalternant systems) are calculated using local semiempirical coupled-cluster theory. The peculiarity of the approach is the use of local ethylene π-molecular orbitals to represent double bonds in the molecule (cue-CCSD approach). The size-limit values of the (hyper)polarizabilities for different types of nonalternant oligomers obtained in the calculations show a significant dependence on the molecular structure. The effect of the electron correlation in the hyperpolarizability calculations is investigated using different levels of the coupled-cluster method including the simplest CCSD model and other models up to the model where the correlation effects due to all four electron excitations are accounted for, as well as with the full configuration interaction model.