Consistent representation of vapor phases in phase field crystal dynamics

Accurate exploration of processes involving interactions among defects, voids, and density shrinkage in rapid solidification requires the ability to simulate phase transformations over large density ranges. We begin this work by presenting a number of numerical artifacts that arise in previous attempts to model the dynamics of solid-liquid-vapor interactions using phase field crystal (PFC) models based on a single density field coupled to its mean field. We then propose a new PFC formalism for modeling solid-liquid-vapor systems that self-consistently couples two components of the density field, one varying on the usual atomic length-scales, the other on scales much greater than the atomic lattice constant. It is shown that the new formalism is free of the aforementioned artifacts exhibited by previous PFC models. We generalize this new solid-liquid-vapor PFC model to alloys and demonstrate its utility through the nucleation of voids in both a fully solid material and during solidification into a liquid.