Formation of the central vacancy in icosahedral Lennard-Jones clusters

The central vacancy has been found in different kinds of icosahedral atomic clusters. For Lennard-Jones (U) clusters, it is studied by optimizing the configurations of LJ561-922 clusters based on two kinds of icosahedral lattices, with and without the central vacancy, and genetic algorithm (GA). By comparing the energies of the clusters with the same size, the results show that the first icosahedral cluster with the central vacancy is LJ585, subsequently, the two configurations are coexistent, then, the optimal configurations with the central vacancy are predominant when the cluster size is larger than 690, and finally, all the clusters with more than 752 atoms are icosahedral configurations with the central vacancy. Furthermore, it is also found that, apart from the compression of outer shells, the symmetry of the configuration of the outermost shell also plays a key role in determining the formation of the central vacancy. Because of the formation of the central vacancy, a new lowest energy sequence of icosahedral LJ clusters is proposed. (C) 2004 Elsevier B.V. All rights reserved.