Image approximation to the reaction field

The reaction field for a charge at an arbitrary position in a spherical cavity in a medium of dielectric constant ε may be expressed in terms of the electrical potential of a certain image charge. For ε τ 1 the potential of the reaction field in the cavity is quite accurately the same as the electrical potential of the image charge. These observations form the basis of a rather economical and accurate way to calculate the reaction field's contribution to the interaction potential of particles with electric moments within a cavity within a dielectric. The results promise to be useful in the study of models for polar fluids and solutions by the Monte Carlo and Molecular Dynamics methods.