Polarizability calculations with the SCF method. IV. Various conjugated hydrocarbons

We calculate the third-order nonlinear electrical polarizabilities of a group of 16 conjugated hydrocarbon molecules with 8 to 14 carbon atoms by making use of the Pariser–Parr–Pople method. We find that the results are quite different from values that were derived previously from the Hückel method. The new values of the space-averaged third-order susceptibilities γ are all positive. The largest γ values are predicted for naphthoquinodimethane-2,6 and for the conjugated hydrocarbon chains, in particular, for tetradecaheptaene.