J. P. Valleau and R. Ivkov

Chemical Physics Theory Group, Lash Miller Chemical Laboratories, University of Toronto, Toronto, Ontario, Canada M5S 1A1

G. M. Torrie

Department of Mathematics and Computer Science, Royal Military College, Kingston, Ontario, Canada K7K 5LO

Monte Carlo methods are presented for the evaluation of the various components of the force between parallel charged surfaces due to the presence between them of an electrolyte, represented by the restricted primitive model. This is a significant problem because some recent theoretical results, and computations on even simpler models, have put in question the adequacy of traditional Derjaguin–Landau–Verwey–Overbeek （DLVO） theory in offering a basic understanding of colloid stability. The methods are applied principally to 2:2 electrolytes at a variety of surface charge densities. We find, in contrast to DLVO theory, that the force between the surfaces resulting from the electrolyte is almost everywhere attractive; in detail these forces turn out to have a remarkably rich behavior resulting from the interaction of their various contributions. The results bolster the perception that we need to take a new look at some basics of colloid science. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.