  The restricted primitive model with nonadditive hard-sphere diameters is
shown to have interesting and peculiar clustering properties. We report
accurate calculations of the cluster concentrations. Implementing efficient and
ad hoc Monte Carlo algorithms we determine the effect of nonadditivity on both
the clustering and the gas-liquid binodal. For negative nonadditivity, tending
to the extreme case of completely overlapping unlike ions, the prevailing
clusters are made of an even number of particles having zero total charge. For
positive nonadditivity, the frustrated tendency to segregation of like
particles and the reduced space available to the ions favors percolating
clusters at high densities.
