Hückel Model Calculations of Polarizability and Hyperpolarizability for Conjugated Molecules

We have conducted a theoretical evaluation of the linear and nonlinear polarizabilities of various hydrocarbon compounds using perturbation theory of the Huckel Hamiltonian. We have found that for polyene chains the alternation of carbon-carbon bond lengths is a crucial feature. Secondly, we have found that for halogen substituted benzene molecules, the inclusion of differential overlap is essential to reproduce the trend in the hyper-polarizability that is observed in experiment. This contrasts with the standard result that differential overlap produces no qualitative change for pure hydrocarbon molecules.