Phase behaviour in binary mixtures of ultrasoft repulsive particles

Abstract

We investigate the phase behaviour of binary mixtures consisting of two ultrasoft species labeled 1 and 2, using the liquid-state theory and the classical density functional theory. The interaction potentials of the two species belong to different classes of ultrasoft potentials that display a dramatically different phase behaviour in the pure case: in the pure species-1 system, there is a maximum freezing temperature and re-entrant melting occurs; in the pure species-2 system, freezing to a cluster-crystal phase, defined by multiple occupancy of each lattice site, occurs at all temperatures. We examine the phase behaviour in the mixture for different potential parameters. In some cases we find that the clustering behaviour of species 2 can induce clustering of species 1 in 2-rich systems. We identify and characterise stable crystal structures and investigate the effect of a nearby demixing transition on the liquid-solid phase coexistence.