STRUCTURE OF 2-COMPONENT CLUSTERS

Phase separation in binary liquid Lennard-Jones clusters is investigat ed employing computer simulation methods. Clusters ranging in size fro m 50 to 240 particles are considered with special emphasis on systems with equal numbers of A and B particles. Cluster morphology is systema tically explored by varying the ratios, alpha=epsilon(AB)/epsilon(AA), beta=epsilon(BB)/epsilon(AA), Gamma=sigma(AB)/sigma(AA), and Delta=si gma(BB)/sigma(AA), where sigma and epsilon are the Lennard-Jones size and energy parameters. A detailed alpha,beta ''phase diagram'' is pres ented for the case Gamma=Delta=1. Stable phase separated clusters are shown to fall into two general classes: elongated clusters of cylindri cal or dumbbell shape, the ends of which are A-rich and B-rich phases, and spherical coated clusters consisting of a core of one species coa ted by the other. More quantitative structural information is given in the form of interfacial density profiles. We also propose two theoret ical models for phase separation in binary clusters. One is a simple m acroscopiclike droplet approach and the other is a mean field lattice model. Both simple models capture many of the important physical featu res observed in the computer simulations. Together they provide insigh t into the nature of phase separation in small systems.