We review the bond-boost method for accelerated molecular dynamics (MD) simulation and we demonstrate its application to kinetic phenomena relevant to thin-film growth. To illustrate various aspects of the method, three case studies are presented. We first illustrate aspects of the bond-boost method in studies of the diffusion of Cu atoms on Cu(001). In these studies, Cu interactions are described using a semi-empirical embedded-atom method potential. We recently extended the bond-boost method to perform accelerated ab initio MD (AIMD) simulations and we present results from preliminary studies in which we applied the bond-boost method in AIMD to uncover diffusion mechanisms of Al adatoms on Al(110). Finally, a problem inherent to many rare-event simulation methods is the 'small-barrier problem', in which the system resides in a group of states connected by small energy barriers and separated from the rest of phase space by large barriers. We developed the state-bridging bond-boost method to address this problem and we discuss its application for studying the diffusion of Co clusters on Cu(001). We discuss the outlook for future applications of the bond-boost method in materials simulation.
Using first-principles calculations based on density-functional theory, we elucidate mechanisms and energy barriers for atomic diffusion on Al͑110͒, Al͑100͒, and Al͑111͒, up and down ͑100͒ and ͑111͒ steps on Al͑110͒, and between the ͑100͒, ͑111͒, and ͑110͒ facets of Al. We find that the energetically preferred mechanism for adatom diffusion on Al͑110͒ is a diagonal exchange between the adatom and the substrate, which leads to isotropic diffusion on this anisotropic surface. Similarly, diagonal exchange involving three atoms is the preferred mechanism for atoms to ascend and descend the ͑100͒ and ͑111͒ steps. The descent of atoms over the ͑100͒ steps is hindered by diffusion to the step edge while for the ͑111͒ steps, it is hindered by diffusion over the edge. Energy barriers to ascend from ͑110͒ to ͑100͒ or ͑111͒ facets depend on facet height. Neighboring adatoms can significantly influence diffusion-energy barriers and simple approaches cannot predict this complex behavior. The energy barriers for dimers to climb from the ͑110͒ to the ͑100͒ and ͑111͒ facets are lower than those for isolated adatoms.
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