Direct calculation of solid-vapor coexistence points by thermodynamic integration: Application to single component and binary systems

Abstract

We present a new thermodynamic integration method that directly connects the vapor and solid phases by a reversible path. The thermodynamic integration in the isothermal-isobaric ensemble yields the Gibbs free energy difference between the two phases, from which the sublimation temperature can be easily calculated. The method extends to the binary mixture without any modification to the integration path simply by employing the isothermal-isobaric semigrand ensemble. The thermodynamic integration, in this case, yields the chemical potential difference between the solid and vapor phases for one of the components, from which the binary sublimation temperature can be calculated. The coexistence temperatures predicted by our method agree well with those in the literature for single component and binary Lennard-Jones systems.

Nonmonotonic Dependence of the Absolute Entropy on Temperature in Supercooled Stillinger-Weber Silicon

“…We computed the excess Gibbs free energy difference G e = G HDL − G crystal between the HDL and the crystal phases, by applying the constrained fluid λ integration method [14] in the isothermalisobaric ensemble [5,6,4]. Recently, the method was found to predict the melting point of SW silicon accurately [3].…”

“…In this work, we study equilibrium HDL phases at and above 1060 K in isothermal-isobaric (NPT) Monte Carlo (MC) simulations at zero pressure, focusing particularly on the volume (or density) distributions. We find that due to shallow free energy barriers, complete equilibration of the HDL phase cannot be achieved in some MC trajectories, leading to non-equilibrium states at 1060 K. We have used a recently developed thermodynamic integration method [14,5,6,3] to measure precisely the excess Gibbs free energy (G e ) of the HDL phases with respect to the crystalline phases at a given temperature and pressure. These computations yield information about the entropy changes in the HDL phases as the temperature is decreased to 1060 K. Our work provides further insight into the transition from the HDL phase to the low density phases near 1060 K. In what follows, we describe the details of our computational method.…”