Free energy calculations for solid solutions by computer simulations

Two techniques for calculating the free energy in a binary solid solution of hard spheres are presented. Both compute the free energy difference between a monodisperse system and the mixture. A reversible path is constructed from the solid solution to the monodisperse system—in one case by varying the composition and in the other by changing the diameter ratio. The relative merits of the two methods are discussed. We find that the technique in which the diameter ratio is changed appears more efficient. Examples of application of each technique are presented.