Rare event calculations for nanosystems : diffusions, dislocations and configurational changes of CNTs

Abstract

Action-derived molecular dynamics (ADMD) calculations are executed to typical examples of rare event systems in nanoscale; Surface diffusion and coalescence of carbon nanostructues. In the studies of the surface diffusion, the activation energy barriers during basic diffusion mechanisms of single adatom are examined. For this, we employ six different metal elements and three different surfaces with low Miller indices, and compare the numerical results. The strain effect on the barriers of basic mechanisms and correlated diffusions of a few adatoms are evaluated as well. In addition, we investigate the diffusions related with steps and step corners on the three different surfaces, which have close relations with the growth and shape of islands on the surface. Finally, we inspect the possibility of the combination of the multiscale schemes in spatial and temporal domains simultaneously, by adopting the ADMD into a quasicontinuum model. Next, we investigate the microscopic merging and junction formation mechanisms of two carbon nanotubes and find out the most favorable dynamic pathways of the reactions. The global and local activation energy barriers are evaluated during the dynamic pathways of the coalescence and junction formation. By introducing additional carbon atoms, an autocatalytic effect, reducing the activation energy barrier of the reactions, of additional carbon atoms on the coalescences of fullerenes and carbon nanotubes are shown as well. In addition to the topics mentioned above, the energetics and mobility of dislocations in the crystal structures are analyzed through the molecular statics and the ADMD calculations. The core structure of dislocations in a face-centered cubic and a diamond crystal are visualized in atomic scale. The changes of system energy due to a dislocation pair are investigated under various conditions. We implement ADMD to the mobility of dislocation cores and examine the Peierls energy, which is the activation energy ba...