POLARIZABILITY AND HYPERPOLARIZABILITY OF INFINITE CONJUGATED POLYMERS

From a technological point of view one of the promising aspects of the conjugated polymers is their large nonlinear optical responses. It ha s been shown experimentally that the nonlinear polarizability per unit cell of conjugated oligomers as a function of chain length first reac hes the saturation for oligomers containing a large number of monomers . Thus, in order to study the properties of polymers theoretically, it is useful to consider infinite chains. In the present work, we report results of parameter-free, first-principles, density-functional studi es of the polarizability, the hyperpolarizability, and other electroni c properties of isolated trans polyacetylene and polycarbonitrile for DC fields perpendicular to the chain axis. The influence of a heteroat om (nitrogen) on these properties is thereby exemplified.