  We introduce a one-parameter family, $0 \leq H \leq 1$, of pair potential
functions with a single relative energy minimum that stabilize a range of
vacancy-riddled crystals as ground states. The "quintic potential" is a
short-ranged, nonnegative pair potential with a single local minimum of height
$H$ at unit distance and vanishes cubically at a distance of $\rt$. We have
developed this potential to produce ground states with the symmetry of the
triangular lattice while favoring the presence of vacancies. After an
exhaustive search using various optimization and simulation methods, we believe
that we have determined the ground states for all pressures, densities, and $0
\leq H \leq 1$. For specific areas below $3\rt/2$, the ground states of the
"quintic potential" include high-density and low-density triangular lattices,
kagom\'{e} and honeycomb crystals, and stripes. We find that these ground
states are mechanically stable but are difficult to self-assemble in computer
simulations without defects. For specific areas above $3\rt/2$, these systems
have a ground-state phase diagram that corresponds to hard disks with radius
$\rt$. For the special case of H=0, a broad range of ground states is
available. Analysis of this case suggests that among many ground states, a
high-density triangular lattice, low-density triangular lattice, and striped
phases have the highest entropy for certain densities. The simplicity of this
potential makes it an attractive candidate for experimental realization with
application to the development of novel colloidal crystals or photonic
materials.
