Ab initio investigation of the sum-frequency hyperpolarizability of small chiral molecules

Using a sum-over-states procedure based on configuration interaction singles /6-311++G^**, we have computed the sum-frequency hyperpolarizability β_ijk(-3ω;2ω,ω) of two small chiral molecules, R-monofluoro-oxirane and R-(+)-propylene oxide. Excitation energies were scaled to fit experimental UV-absorption data and checked with ab initio values from time-dependent density functional theory. The isotropic part of the computed hyperpolarizabilities, β̄(-3ω;2ω,ω), is much smaller than that reported previously from sum-frequency generation experiments on aqueous solutions of arabinose. Comparison is made with a single-centre chiral model.