Molecular dynamics study of the structure and thermodynamic properties of argon microclusters

Microclusters of 2–100 argon atoms were studied using molecular dynamics. The microclusters were ordered solids at low temperatures and energies and disordered liquids at high temperatures and energies. The melting transition occurred considerably below the bulk melting temperature. Radial density functions, interference functions, diffusion coefficients, and surface energies were calculated for both the solid and liquid phases. The surface energies of the microclusters could be expressed as a function of the form Ai2/3+Bi1/3 where i is the number of atoms in the cluster. For 0 °K solid clusters A and B have the values 0.26×10−12 and −0.12×10−12 erg, respectively; for liquid clusters at 40 °K, A and B have the values 0.17×10−12 and −0.045×10−12 erg, respectively. Clusters containing 7 or more atoms melted with the occurence of a first-order-like transition. This transition was studied further through Monte Carlo calculations. A possible model for the first-order-like transition is proposed.