Density Expansions of the Reduced Distribution Functions and the Excess Free Energy for Plasma with Coulomb and Short-Range Interactions

The equilibrium properties of a multi-component plasma of charged particles that interact through the Coulomb potential and general short-range potentials are investigated at low density within the framework of classical statistics. In particular, this article presents density expansions of (1) the reduced distribution functions for two and more particles up to second order as obtained from the screened Bogoliubov-BornGreen-Kirkwood-Yvon hierarchy and (2) the interaction contribution to the Helmholtz free energy including a new closed representation of the fourth cluster integral derived with the help of a usual charging procedure.