On the Theory of Dielectric Polarization

Abstract

The polarization of a nonpolar dielectric in a homogeneous field is investigated from a molecular point of view. A statistical calculation of the average local field in a molecule shows that fluctuations in the induced molecular moment give rise to a deviation from the Lorentz field. As a result, small but significant deviations from the Clausius‐Mosotti formula are to be expected. A series expansion for (ε—1)v/3 of the following form is obtained $${\text{(ε−1)v/3=P}}_0{\text{[1+(1+γ+σ)P}}_0\mathrm{/v+···],}$$ where ε is the dielectric constant, v the molal volume and P₀ the molecular polarization. The coefficients in the corresponding expansion of the Clausius‐Mosotti formula are all equal to unity. The correction γ, arising from translational fluctuations, is about 0.1 for most substances. The correction σ depends upon the optical anisotropy of the molecule and its shape.