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 has been shown experimentally that the nonlinear polarizability per unit cell of conjugated oligomers as a function of chain length first reaches 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 studies of the polarizability, the hyperpolarizability, and other electronic properties of isolated trans polyacetylene and polycarbonitrile for DC fields perpendicular to the chain axis. The influence of a heteroatom (nitrogen) on these properties is thereby exemplified.