The influence of boundary conditions used in machine simulations on the structure of polar systems

Studying generalized Onsager models the effect of boundary conditions (finite volume and potential cut-off), used in machine simulations, on the structure of polar systems is examined critically. It is found that deviations from the infinite-system structure stem primarily from the truncation of the potential, which is by no means equivalent to a finite volume, as assumed so far. Intended originally to model computer-generated R-dependent Kirkwood g-factors, continuum theory also predicts correctly the qualitative shape of h Δ- and hD -curves, reported in [10] for various geometries. The present analysis enables, for the first time, a physical understanding of the influence of the cut-off. It turns out that the mean electrostatic energy is only slightly affected and that the asymptotic value of Gk (R) profits from a cancellation of errors. An improved relation is given for the volume dependence of <M 2>. Within the framework of our models one can also understand rigorously the origin of Barker's reaction field.