Phase diagrams of complex systems with nested sampling

The nested sampling method provides an efficient way of computing the classical partition function, and from it thermodynamic quantities and other observables as a function of temperature and pressure. It can therefore be used to calculate temperature dependent properties and phase diagrams. We show how nested sampling can be applied to two systems with chemical and structural complexity. The first is polymers, which have both short range (bond length, angle) and long range (conformation, dense packing in the melt/solid) structure, which we model with chemicaly specific coarse-grained potentials. We show how to explore configuration space given the form of typical coarse-grained models, and present results for their phase diagrams. The second is multicomponent systems, which can exhibit phase separation in some parts of the phase diagram, e.g. a two-phase coexistence region delimited by a liquidus at high T and solidus at low T for the liquid-solid transition in a binary alloy. We discuss several approaches to handling this tendency to phase separation, and demonstrate that we can efficiently compute phase diagrams for multicomponent systems.