Behavior of icosahedral clusters in computer simulated hard sphere systems

The model of densely packed hard spheres is used as a first-order approach to the structure of liquid metals and liquid metallic alloys. The concept of local packing fraction is applied to characterize the local structure. Starting from dilute systems of randomly distributed spheres, densification does not lead to the formation of local icosahedral order. A second type of initial structures consisting of icosahedral clusters embedded in a system of randomly packed hard spheres is also analyzed. Densification of such systems leads to a continuous retrogression of the degree of local icosahedrality, and the frequency distribution of local packing fraction approaches that of the arrangements obtained by densification of uncorrelated random initial structures. We conclude that global densification and formation of icosahedral clusters with high local packing fraction are competing processes in hard sphere systems.