THE LOCAL FIELD DISTRIBUTION IN A FLUID

The distribution of potentials or fields felt at any given point in a liquid (the local field distribution) ends up being the crucial element in calculating quantities ranging from the inhomogeneous broadening of spectral lines to the rates of irreversible electron transfer. Indeed, the usefulness of this distribution in even its simplest form, the version which assumes a completely uncorrelated environment, has long been appreciated. However, there are a number of difficulties with this version. When the fluid density is low enough to make a neglect of correlations reasonable, the distribution function can still be awkward to calculate numerically. Much more seriously, the omission of correlations among the surrounding atoms is totally unrealistic in a dense liquid. We show here that it is possible to arrive at expressions for the local field distribution that are both accurate under dense liquid conditions and are straightforward to evaluate numerically. The key to this development turns out to be the recognition that the short-ranged and long-ranged contributions to the local field play qualitatively different roles - which can be separated formally using a device we call a closest particle expansion. The qualitative differences between the results for correlated and uncorrelated particles are discussed, as is the appropriateness of the commonly used Gaussian approximation. © 1990 American Institute of Physics.