The structure of liquid clusters of Lennard-Jones atoms

Abstract

We have performed computer simulations of atomic clusters with the goal of studying the structure of the liquid phase. Classical constant energy molecular dynamics was used, with the atoms interacting via a Lennard-Jones 6-12 potential. Liquid clusters were formed by evaporation from a lattice with a relatively large lattice constant; for comparison, solid clusters were formed by a 10–15% scaling of the coordinates of the minimum-energy configurations. The liquid clusters formed ranged in size from approximately 50 to 1000 atoms. The liquid radial distribution functions [ g( r)] show a split second peak (which is sometimes attributed to “glassy” behavior) which becomes much less pronounced as the size increases. A common neighbour analysis shows a high degree of local polytetrahedral ordering in the liquid and only a very small amount of local octahedral order, in contrast to the solid g( r). Radial density profiles [ ρ( r)] of the liquid clusters show a very clear radial layering; the layer separation is approximately the repulsive hard core diameter. For the larger clusters, the layering is progressively less pronounced, and nearly absent for the largest cluster studied (1085 particles). In two cases, the cluster began in a liquid state which persisted long enough for structural quantities to be taken [ g( r) and ρ( r)] but then showed evidence of the onset of solid structure. Mean squared displacements resolved into interior/exterior of the cluster show that there is a strong spatial dependence of the diffusion in the smaller liquid clusters.