A statistical formulation is presented for the reaction and cavity-field response functions of an isotropic nonpolar substance. It is shown that the reaction-field approach can be made consistent to a good approximation with statistically calculated fields by a reasonable choice of the cavity radius a. The cavity radius is a complicated function of density, temperature, and molecular parameters and, in first approximation, is given by expression a−3= ∫ 0∞3r−4ρ(r)dr,where ρ(r) is the radial distribution function. The value of a3 computed for liquid Xe from x-ray scattering data according to the latter formula is found to be equal to ½σ3, where σ is the Lennard-Jones collision diameter; this value is in very good agreement with the Böttcher—Onsager value for a3 calculated on the basis of the macroscopic dielectric constant and polarizability of the free molecule. The dielectric and statistical reaction and cavity-field functions are compared and discussed.

Effects of van der Waals interactions on molecular dipole moments: The role of fieldinduced fluctuation correlations J. Chem. Phys. 83, 5198 (1985); 10.1063/1.449732Remarks on the magnitude of van der Waals induced dipole moments in physisorption Expressions are derived for calculating the induced dipole moment of an arbitrary molecule A interacting with an arbitrary system B through first-and second-order Coulomb interaction. The theory is formulated in terms of linear and quadratic charge-density susceptibilities and takes account of charge penetration but not exchange between the systems. The theory is specialized to the interaction of two nonoverlapping molecules and to a molecule interacting with a nonferroelectric solid, metallic, or crystalline. In the case of two interacting molecules, the induced moment is developed in inverse powers of R, the distance between the centers of the molecules, up to and including R -7; the coefficients of the series are given in terms ofthe total charges, permanent moments, polarizabilities, and hyperpolarizabilities. In the case of the solid, the results are given in terms of the molecule-solid distance Zo, the dielectric function of the solid, and the permanent moments, polarizabilities, and hyperpolarizabilities of the molecule. The expressions for the dispersion and induction dipoles derived here in terms of the charge-density (hyper) susceptibilities are the most general to date in that ionic contributions are included, and the expansion in terms of the (hyper)polarizabilities is the most explicit for nonoverlapping systems. Our results are compared with the work in the literature.

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A theory is presented whereby the long-range intermolecular forces, including the London dispersion forces, of pure nonelectrolytes may be calculated from optical and dielectric data. The method is based on the continuum-model approach, where one molecule is treated explicitly while the others are replaced by a medium of uniform dielectric. The classical and quantum-mechanical oscillators are used as working models and expressions are derived for computing the cohesive energy appropriate for both types of oscillators. The potential energy based on the quantum-mechanical oscillator is calculated for a number of liquids and is shown to be in fair agreement with the experimental energy of vaporization.

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