The Local Field and What It Means

The easy link between the dielectric constant of isotropic media and the molecular polarizability of the constituents, is traditionally given by the Lorentz-Lorenz (LL) relation. The local field concept however upon which this relation is based, needs to be re-examined for highly inhomogeneous systems, like surfaces and interfaces. Local fields belong inherently to discrete dipole models, but for the comparison with continuum approaches only descriptions based on average fields, are the more suited ones. This holds particularly for the comparison with the Fourier-type solution of the continuum problem, upon which the classical Adler and Wiser papers [1, 2] are based.