True mixture versus effective one component fluid models of asymmetric binary hard sphere mixtures: a comparison by simulation

The pair distribution function of solute particles determined by simulation of true mixtures with diameter ratios of 5, 10 and 20 is compared with that obtained in their representation by effective one-component fluids with pairwise additive interactions. The pair distribution function near contact is found to be overestimated by the effective fluid approach, for all size ratios. In the domain of the phase diagram accessible to the simulation algorithm, the deviation is found to be moderate. Its consequences for the coexistence lines are discussed.