Analytical approach to the thermodynamics and density distribution of crystalline phases of hard spheres

We extend the well-known free-volume approach to describe the thermodynamic properties and density distribution of crystalline phases of hard hypersph ere systems. Despite its extreme simplicity the approach yields results whi ch are in quantitative agreement with simulation data. The theory can, in p articular, describe the properties of the body-centred cubic phase of hard spheres, for which density-functional approaches provide unphysical results , allowing for the application of perturbation theory to situations where, as is the case in some colloidal systems, the body-centred cubic is one of the most interesting phases. The theory is also tested by applying it to sy stems of hard discs.