  The Voronoi cell of any atom in a lattice is identical. If atoms are
perturbed from their lattice coordinates, then the topologies of the Voronoi
cells of the atoms will change. We consider the distribution of Voronoi cell
topologies in two-dimensional perturbed systems. These systems can be thought
of as simple models of finite-temperature crystals. We give analytical results
for the distribution of Voronoi topologies of points in two-dimensional Bravais
lattices under infinitesimal perturbations and present a discussion with
numerical results for finite perturbations.
