Structure and dynamics in a monolayer of core-softened particles

The structure and dynamics of a monolayer of spherical core-softened particles are studied using Monte Carlo and molecular dynamics computer simulations. The pair interaction potential is constructed from the Lennard-Jones potential plus a long-range repulsion varying like 1-3, where r is the interparticle separation. The model loosely mimics a monolayer of colloidal magnetic particles at an interface, with a magnetic field applied perpendicular to the plane. With an appropriate choice of parameters the potential is purely repulsive, and possesses a repulsive shoulder with a stationary point of inflection; this is an example of a core-softened potential. Monte Carlo simulations have been used to show that at low temperature the fluid phase exhibits a remarkable array of clusters with structural motifs including dimers, chains, stripes, and octagonal rings. At high density the system crystallizes first into a kagome net, and then into a close-packed triangular lattice. The dynamical properties of the fluid phase have been investigated using molecular dynamics simulations. An examination of the longitudinal and transverse current correlations and the dispersions of the collective modes shows that there are very well resolved 'intracluster' and collective motions. (C) 2006 Elsevier B.V. All rights reserved.