  The problem of successfully simulating ionic fluids at low temperature and
low density states is well known in the simulation literature: using
conventional methods, the system is not able to equilibrate rapidly due to the
presence of strongly associated cation-anion pairs. In this manuscript we
present a numerical method for speeding up computer simulations of the
restricted primitive model (RPM) at low temperatures (around the critical
temperature) and at very low densities (down to $10^{-10}\sigma^{-3}$, where
$\sigma$ is the ion diameter). Experimentally, this regime corresponds to
typical concentrations of electrolytes in nonaqueous solvents. As far as we are
aware, this is the first time that the RPM has been equilibrated at such
extremely low concentrations. More generally, this method could be used to
equilibrate other systems that form aggregates at low concentrations.
