Effective forces between macroions: a Monte Carlo study

The effective forces between two spherical highly charged colloidal macroions are calculated within the primitive model of strongly asymmetric electrolytes using Monte Carlo simulations. For typical parameters corresponding to aqueous suspensions of polystyrene spheres, the forces are found to be repulsive over a broad range of distances between the macroions. Our results are in semi-quantitative agreement with different variants of linear screening theory. A recently developed cumulant expansion, however, fails in predicting the correct sign of the effective forces.