Defect kinetics on experimental timescales using atomistic simulations

In his last few years, Patrick Veyssiere became involved in atomic-scale molecular dynamics simulations that give access to the full atomistic details of dislocation/dislocation and dislocation/defect interactions. Such simulations are, however, very limited in time and do not allow the study of diffusional processes, such as vacancy migration. For such processes, one needs to explore the configuration space in search of activated states, whose energy barriers control the slow thermal-activated kinetics of defects. Here, we present work, performed in the context of a FranceChina project and initiated by Patrick Veyssiere, where we study the long-term evolution of vacancy supersaturations in fcc metals. We employed a combination of saddle-point search methods (activationrelaxation technique, automated basin climbing method and nudged elastic band method) and kinetic Monte Carlo simulations to reach experimental timescales while retaining atomistic fidelity. The simulations identified a specific and, so far, unidentified cluster, the pentavacancy, made of five vacancies forming a bcc unit cell in the fcc lattice, which plays a central role in vacancy clustering in aluminium.