  We examine the effect of vacancies on the phase behavior and structure of
systems consisting of hard cubes using event-driven molecular dynamics and
Monte Carlo simulations. We find a first-order phase transition between a fluid
and a simple cubic crystal phase that is stabilized by a surprisingly large
number of vacancies, reaching a net vacancy concentration of ~6.4% near bulk
coexistence. Remarkably, we find that vacancies increase the positional order
in the system. Finally, we show that the vacancies are delocalized and
therefore hard to detect.
