On the Theory of Dielectric Polarization

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 (ε−1)v/3=P0[1+(1+γ+σ)P0/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.