MONTE-CARLO STUDIES OF A 2-DIMENSIONAL COMMENSURATE INCOMMENSURATE SYSTEM - EFFECTS OF CHANGE OF PARTICLE-SIZE AND INTERACTION PARAMETERS AT CONSTANT NUMBER DENSITY

A model two-dimensional system consisting of Lennard-Jones particles adsorbed onto a structured continuum surface has been examined for various values of the particle diameter, the potential barrier impeding movement along the surface, and the strength of the intermolecular interaction epsilon*. The degree of commensuration as measured by the mean distance of the particles from the nearest lattice site shows a minimum when plotted against epsilon*, this minimum being very sensitive to the size of the particles. Where the particles are so large that the system is near close-packed the behaviour becomes more complicated with evidence for the existence of a state intermediate between the commensurate (C) and incommensurate (IC) states. In this intermediate state (I) the molecules tend to be commensurate with respect to one axis of the lattice but not with respect to the other. Domains of the two possible kinds of intermediate state (commensurate with respect to the x- or y-axis) are observed in snapshots.