The Importance of Treating Electron-Electron Interactions in the Calculation of Dynamic Third-Order Polarizabilities for Linear Conjugated Polyenes

ABSTRACTThe non-resonant electronic component of γ(-3ω ω, ω, ω) is calculated for ethylene, all-trans 1,3-butadiene, all-trans 1,3,5-hexatriene, and all-trans 1,3,5,7- octatetraene. The γ(-3ω; ω, ω, ω) is evaluated using the sum-over-states method and the all-valence-electron, semi-empirical INDO-SCF-MO procedure combined with single- and double-excitation configuration interaction (CI). The treatment of electron-electron interactions at the level of only single-excitation CI calculates negative values of γ(-3ω ω, ω, ω), which are in disagreement with measured positive values. The treatment of the interactions at the level of single- and double-excitation CI correctly calculates positive values for γ(-3ω ω, ω, ω). We conclude that the treatment of electron-electron interactions at least at the level of single- and double-excitation CI is needed to properly describe the dynamic thirdorder polarizabilities of linear conjugated polyenes, and related molecules with π-electron bonding networks.