An attempt to bridge the gap between computation and experiment for nonlinear optical properties: Macroscopic susceptibilities in solution?

We present a new methodology, working within the framework of the Polarizable Continuum Model, that derives quantities directly comparable with data from nonlinear optical (NLO) experiments on liquid solutions through computed molecular properties. The procedure does not require any knowledge of preliminary experimental data (as do some semiempirical methods) but permits one to obtain the final molar property (specifically, the macroscopic susceptibilities) in terms of effective molecular dipoles and (hyper)polarizabilities. The latter are obtained through an ab initio description of the molecule of interest when it is mutually interacting with the surrounding medium, which is represented by a continuum dielectric. Numerical applications, and the related comparisons with experiments, are presented for refractive and pemittivity first-order processes and for third-order EFISH (electric-field-induced second harmonic generation) experiments for 4-nitroaniline (pNA) and 3,5-dinitroaniline (3,5-DNA) in liquid dioxane at room temperature.