Free energy and phase equilibria of solids by molecular simulation

A new and efficient method for determining the free energy of solids has been investigated here. This method is a modification of the Bennett's method. This method was found to have considerable success when applied to the Lennard-Jones crystal, whose free energy is better determined by this simulation method than from the Lattice Dynamics calculations when both are compared to the known equation of state. However, the free energy of the hard sphere system is not as successfully determined by this method indicating that the choice of the reference system is an important factor in the success of the method.; Knowledge of the free energy of solids is important in phase equilibria calculations involving solid phases such as those modeled by the triangle-well potential model. The next-simplest model, after the square-well model, that exhibits attractive interactions is the triangle-well potential model. This study provides Monte Carlo simulation data for the phase diagram of the triangle-well model for different interaction ranges. Both the solid-fluid and vapour-liquid phase behavior has been considered, and instances of polymorphism are noted when they arise. Simulation results are used to examine the ability of simple perturbation-theory models to characterize the behavior. The phase behaviour is much less rich than that observed in the less realistic square-well model.; The solid phase solubility diagram of compound semiconductor alloys has been studied here using Monte Carlo simulation techniques. The state of the art in studying such alloys has been using a molecular model such as the Valence Force Field model along with an untested assumption that the alloy follows the regular solution theory. Various simulation methods were investigated to determine the phase diagram, the transition matrix Monte Carlo method proved to be most successful. The transition matrix Monte Carlo method is used to establish the phase diagram. Data are compared with the existing regular-solution modeling efforts, which are based on the same molecular model. Structural properties such as bond length and the local composition of the constituents of ternary alloy systems are determined using simulation and compared to experimental observations where available for the same.