title: Phase coexistence of cluster crystals: beyond the Gibbs phase rule.
abstract: We report a study of the phase behavior of multiple-occupancy crystals through simulation. We argue that in order to reproduce the equilibrium behavior of such crystals, it is essential to treat the number of lattice sites as a constraining thermodynamic variable. The resulting free-energy calculations thus differ considerably from schemes used for single-occupancy lattices. Using our approach, we obtain the phase diagram and the bulk modulus for a generalized exponential model that forms cluster crystals at high densities. We compare the simulation results with existing theoretical predictions. We also identify two types of density fluctuations that can lead to two sound modes and evaluate the corresponding elastic constants.
authors.affiliation: Center for Computational Materials Science and Institut für Theoretische Physik, Technische Universität Wien, Wiedner Hauptstrasse 8-10, 1040 Wien, Austria.
authors.forename: Bianca M
authors.initials: BM
authors.lastname: Mladek
authors.forename: Patrick
authors.initials: P
authors.lastname: Charbonneau
authors.forename: Daan
authors.initials: D
authors.lastname: Frenkel