Simulation of phase boundaries using constrained cell models

• Published in: Journal of physics. Condensed matter 2012-09, Vol.24 (37), p.375105-375105
• Main Authors: Nayhouse, Michael, Heng, Vincent R, Amlani, Ankur M, Orkoulas, G
• Format: Article
• Language: English
• Subjects: Computer simulation; Condensed matter; Condensed matter: structure, mechanical and thermal properties; Constraining; Constraints; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Histograms; Phase boundaries; Phase diagrams; Physics; Solid phases
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/24/37/375105

Despite impressive advances, precise simulation of fluid-fluid and fluid-solid phase transitions still remains a challenging task. The present work focuses on the determination of the phase diagram of a system of particles that interact through a pair potential, φ(r), which is of the form φ(r) = 4 [(σ r)2n − (σ r)n] with n = 12. The vapor-liquid phase diagram of this model is established from constant-pressure simulations and flat-histogram techniques. The properties of the solid phase are obtained from constant-pressure simulations using constrained cell models. In the constrained cell model, the simulation volume is divided into Wigner-Seitz cells and each particle is confined to moving in a single cell. The constrained cell model is a limiting case of a more general cell model which is constructed by adding a homogeneous external field that controls the relative stability of the fluid and the solid phase. Fluid-solid coexistence at a reduced temperature of 2 is established from constant-pressure simulations of the generalized cell model. The previous fluid-solid coexistence point is used as a reference point in the determination of the fluid-solid phase boundary through a thermodynamic integration type of technique based on histogram reweighting. Since the attractive interaction is of short range, the vapor-liquid transition is metastable against crystallization. In the present work, the phase diagram of the corresponding constrained cell model is also determined. The latter is found to contain a stable vapor-liquid critical point and a triple point.