The structure of atomic and molecular clusters, optimised using classical potentials

The problem of the determination of the minimum energy configuration of an arrangement of N point particles under the interaction of their interatomic forces is discussed. The interatomic forces are described by classical many body potentials. Different optimisation methods are considered, multi level single link, topographical differential evolution and a genetic algorithm but it is shown that genetic algorithms combined with an efficient local optimisation method is especially quick and reliable for this task. In addition to comparing some different optimisation methods, the structures of clusters of atoms described by interatomic potential functions containing up to a few hundred atoms are calculated including some with some special symmetries. A number of applications are given including covalent carbon and silicon clusters, close-packed structures such as argon and silver and the two-component carbon-hydrogen system

Shallow implantation of 'size-selected' Ag clusters into graphite

We have investigated the implantation of AgN (N = 20–200) clusters into a graphite substrate over the range of energies (E) 0.75–6 keV using molecular dynamics simulations. We find that after implantation the silver clusters remain coherent, albeit amorphous, and rest at the bottom of an open tunnel in the graphite created by the impact. It is found that the implantation depth of the clusters varies linearly as E/N2/3. We conclude that the cluster is decelerated by a constant force proportional to its cross-sectional area. We also identify a threshold energy for surface penetration associated with elastic compression of the graphite substrate