Electron density and atomic relaxation around a vacancy in a small metal particle

The electron density in an ideal vacancy placed at the center of a small Aluminium microparticle has been studied as a function of the number of atoms in the microparticle. In these circumstances one can conclude that the perturbation of the density is localized in the close neighborhood of the vacancy and is nearly independent of the particle size. Then relaxation of the nearest neighbours of the vacancy was allowed. This relaxation was found to be small, but its sign depends on particle size. For particles larger than ～100 atoms the relaxation is towards the vacancy, as for a vacancy in bulk Aluminium. But for smaller particles, the relaxation is away from the vacancy. This relaxation suggests a nontrivial size dependence of the energy of vacancy formation.