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

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 ± and second hyperpolarizability 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 ± and are in good agreement with the corresponding gas-phase experimental values at the same fundamental wavelength. The various values corresponding to different third-order processes exhibit marked difference in their dependence on the conjugation length. For a specific fundamental frequency, the calculated value exhibits the following order: (-3;,,)>(-2;0,,)>(-;,,-) >(-;0,0,)(0;0,,-).