Applicability of the Phase Field Crystal Model in Predicting Phase Diagrams

We have studied the applicability of the Phase Field Crystal (PFC) model Hamiltonian in predicting phase diagrams of binary alloys. The PFC model is a simplified version of the classical density functional theory of freezing. The results presented in this work show that if the interaction parameters of the simple PFC are fitted with microscopic direct correlation functions, the thermodynamic properties of a single component system are predicted wrong. After noting this, we present a new way to obtain the parameters for a one component system. When this procedure is used, the liquid coexistence density becomes fitted correctly, which is a significant improvement to the original fitting procedure. For metal alloys, we have derived a new solution model from the density-functional theory of classical systems, through which the long range interaction coefficients can be fitted to experimental data on mixing Gibbs free energy. However a fitting procedure for the shorter wavelength correlations of an alloy lies beyond the scope of this work. Nevertheless it seems clear that rather than trying to use the model for the calculation of phase diagrams, the experimentally known phase diagrams should be used to fit the correct interaction parameters