Dispersion of linear and nonlinear optical properties of benzene: An ab initio time-dependent coupled-perturbed Hartree-Fock study

Frequency-dependent polarizability a and second hyperpolarizability γ corresponding to various third-order nonlinear optical processes have been calculated by ab initio time-dependent coupled-perturbed Hartree-Fock method. The selection of proper diffuse functions in the basis set is made from a comparison of the calculated values of α(ω) at two optical wavelengths (λ=589 and 632.3 nm) and that of γ(-2ω; 0, ωm ω) at λ = 1064 nm with the reported experimental values at these wavelengths. It is found that a 4-31G basis with a diffuse p and a diffuse d function, in addition to properly describing various elements, yields the values of α and γ which are, respectively, within 7% and 5% of the corresponding experimental results. The in-plane components of α show a larger frequency dispersion compared to the out-of-plane component. The calculated values of γ for the electric field-induced second harmonic generation (EFISH) at five optical wavelengths are within 5%-14% of the reported experimental results. However, a somewhat larger discrepancy between the calculated and measured values of γ for third harmonic generation (THG) and γ for degenerate four wave mixing (DFWM) is found. The order of the γ values for various third-order processes is γ(THG) > γ(EFISH) > γ(DFWM) >γ(EFIKE) ≈γ(EFIOR), where EFIKE and EFIOR, respectively, represent electric field-induced Kerr effect and electric field-induced optical rectification. The elements of γ show deviation from the Kleinman symmetry even at lower optical frequencies.