MOLECULAR DYNAMICS CALCULATIONS OF MICROCLUSTER PROPERTES

Publisher Website
Google Scholar
Abstract
The structural and thermodynamic properties of microclusters in two and three dimensions have been investigated by means of the molecular dynamics technique. This technique in principle produces the atomic configuration of lowest free energy for any given cluster size. The caloric equation of state for the different microclusters were calculated using a truncated Len- nard-Jones pair potential. The nature of the melting transition was investigated and a number of properties, such as melting temperature, latent heat of melting, and premelting phenomena, were found to vary with cluster size, as well as with the structure of the solid phase. 1. Introduction. - Investigations of thermodynamic or structural properties of materials are usually con- cerned with the bulk behaviour, that is the properties that are measured in cases where surface effects are negligible. However, in extreme cases, the presence of a free surface can introduce dramatic deviations from the normal bulk behaviour. Heat capacity measu- rements on thin films in the neighbourhood of the bulk melting point (l), thus reveals that as the film gets thinner, the sharpness of the melting transition as well as the melting temperature decreases progressi- vely. That ,also the structure of a material can be affected by a free surface is known from diffraction experiments on thin films and small particles. Electron diffraction experiments on a number of rare earth metals in the form of evaporated films (2) show that the bulk HCP structure is replaced by an FCC struc- ture when the films are very thin. Electron diffraction studies of microclusters of argon atoms (3) formed by homogeneous nucleation show that the clusters are effectively of the bulk FCC structure, but contain vestiges of noncrystalline structure exhibited by the aggregates in the early stages of their growth. Nume- rous examples of the dependence of physical processes on the properties of very small atom clusters exist, including nucleation and growth, adsorption and catalysis, phase separation and precipitation, super- conduction in thin films, processes in atmospheric physics, and the formation of glasses. The first model which was applied to explain the properties of microclusters is based on the continuum

This publication has 0 references indexed in Scilit: