Statistical mechanics of a positron in a classical fluid

Although the equilibrium theory of classical fluids, simple and complex, has reached the stage of routine accurate evaluation, this is hardly the case for even the next microscopic step, that of a quantum particle in a classical fluid. In many chemical applications, the quantum particle is an electron, but positron annihilation experiments on thermalized positrons and orthopositronium atoms offer a wealth of information to test our theoretical understanding of this general class of systems. Here, we investigate several ways in which the concepts behind classical techniques can be generalized to handle this prototypical quantum problem, in the overt quantum form as well as in the classical polymer representation. Both integral equation and density functional formats are studied and their qualitative characteristics examined.