Evolution of the third-order molecular polarizability in polyenes: A local view from atomic charge derivatives

The origin and chain length evolution of the static third-order polarizability, γ, are discussed in polyenes up to C₈₀H₈₂ via a local analysis of atomic π-orbital electric field-induced polarizations, i.e., of γ charges and their moments. This conceptually and computationally simple approach allows one to obtain a visual representation of the local contributions to γ. The patterns of these local contributions are observed to change qualitatively as a function of chain length; the end parts of the molecule dominate the third-order response at moderate chain lengths, while the contributions from the inner section are responsible for the slow chain-length saturation.