Frequency dependence of linear and nonlinear optical properties of conjugated polyenes: An<i>ab initio</i>time-dependent coupled Hartree-Fock study

Abstract

Using a split-valence Gaussian 4-31G basis function augmented with diffuse p and d function and multiconfiguration self-consistent-field optimized geometries, the frequency-dependent polarizability \ensuremath{\alpha} and second hyperpolarizability \ensuremath{\gamma} of ethylene, trans-butadiene, trans-hexatriene, and trans-octatetraene molecules have been calculated by the time-dependent coupled perturbed Hartree-Fock ab initio method. The calculated values of \ensuremath{\alpha} and \ensuremath{\gamma} are in good agreement with the corresponding gas-phase experimental values at the same fundamental wavelength. The various \ensuremath{\gamma} values corresponding to different third-order processes exhibit marked difference in their dependence on the conjugation length. For a specific fundamental frequency, the calculated \ensuremath{\gamma} value exhibits the following order: \ensuremath{\gamma}(-3\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},\ensuremath{\omega})&gt;\ensuremath{\gamma}(-2\ensuremath{\omega};0,\ensuremath{\omega},\ensuremath{\omega})&gt;\ensuremath{\gamma}(-\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},-\ensuremath{\omega}) &gt;\ensuremath{\gamma}(-\ensuremath{\omega};0,0,\ensuremath{\omega})\ensuremath{\approxeq}\ensuremath{\gamma}(0;0,\ensuremath{\omega},-\ensuremath{\omega}).