Sign change of hyperpolarizabilities of solvated water

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Abstract
The experimental work by Levine and Bethea [J. Chem. Phys. 65, 2429 (1976)] and by Ward and Miller [Phys. Rev. A 19, 826 (1979)] on the hyperpolarizability of solvated water and water in the gas phase, respectively, showed a very substantial effect of the solvent on the measured hyperpolarizability. The sign of the hyperpolarizability of solvated water changed compared to gas phase and the numerical value increased by a factor of 1.5. This article presents a theoretical investigation of the solvent effects of the hyperpolarizabilities and their frequency dispersions for liquid water using the continuum, semicontinuum, and supermolecular models. Calculations involving the semicontinuum and supermolecular models give the sign change of the hyperpolarizabilities, indicating that the hydrogen bonds and the static dipole interaction have substantial impact on the hyperpolarizability of liquid water. Hyperpolarizabilities calculated by the supermolecular approach are about one third of those calculated by the semi-continuum model. The continuum and semicontinuum models involve a recent implementation of a quantum mechanical reaction field response method.