Monte Carlo Estimation of the Free Energy by Multistage Sampling

A method is described for estimating the free energy and entropy of an assembly of particles. This is done by using Metropolis Monte Carlo techniques to generate energy distributions from which we may calculate the absolute volume of configuration space corresponding to a given energy, and thus the configuration integral. One incidentally obtains the thermodynamic quantities over a wide range of reduced temperature. It is particularly easy to apply the method to particles having hard cores, and calculations are reported for hard spheres with Coulombic forces.