  We use computer simulations to study the phase behaviour for hard, right
rhombic prisms as a function of the angle of their rhombic face (the "slant"
angle). More specifically, using a combination of event-driven molecular
dynamics simulations, Monte Carlo simulations, and free-energy calculations, we
determine and characterize the equilibrium phases formed by these particles for
various slant angles and densities. Surprisingly, we find that the equilibrium
crystal structure for a large range of slant angles and densities is the simple
cubic crystal - despite the fact that the particles do not have cubic symmetry.
Moreover, we find that the equilibrium vacancy concentration in this simple
cubic phase is extremely high and depends only on the packing fraction, and not
the particle shape. At higher densities, a rhombic crystal appears as the
equilibrium phase. We summarize the phase behaviour of this system by drawing a
phase diagram in the slant angle - packing fraction plane.
