OPTIMAL EFFECTIVE PAIR POTENTIAL FOR CHARGED COLLOIDS

The effective interaction between charged colloidal particles in solution both with and without added salt is studied using an ab initio theory which includes effective many-body forces induced by the counter- and salt-ions. Fitting these forces with a pair potential, we obtain an optimal pair potential which reproduces the ab initio data for the pair correlations correctly. This optimal potential is very close to a screened Coulomb potential, thus justifying the Yukawa-picture, frequently used for the interaction of charged colloids. In general, however, the effective charge and the screening length differ from that of Derjaguin-Landau-Vervey-Overbeek (DLVO) theory and Wigner-Seitz cell models. Moreover, the optimal effective pair potential depends on the thermodynamic phase. The mapping of many-body interactions onto optimal pair-interactions drastically reduces the computing time in simulating large systems.