Calculation of refractive indices and third-harmonic generation susceptibilities of liquid benzene and water: Comparison of continuum and discrete local-field theories

The refractive indices (linear response) and the nonlinear susceptibility f or third harmonic generation (THG) at lambda =1064 nm of liquid water and b enzene are predicted, using ab initio molecular (hyper)polarizabilities and local-field corrections calculated according to the Lorentz model, the gen eralized reaction-field model of Onsager, and a discrete local-field theory applied to liquid structures obtained by classical molecular simulation me thods. The ratio of the calculated THG susceptibilities for the two liquids is compared with experimental results, in order to avoid ambiguities conce rning the factors used to calibrate the THG experiments. All models are abl e to reproduce the experimental refractive indices of both liquids accurate ly, but are less successful for the THG susceptibility. The discrete local- field corrections for the THG susceptibility are considerably larger than t hose of the continuum model in the form of the more accurate extended react ion-field approach. (C) 2001 American Institute of Physics.