The dynamics of carbon and nitrogen atoms on the Fe_(55) nanoparticle is investigated by means of molecular dynamics simulations at the density-functional tight-binding level. A time range of at most 0.4 ns is covered in the molecular dynamics simulations. Different degrees of adatom coverage are considered. Nitrogen and carbon atoms express different dynamics. Adsorbed monomers and large fragments are rather immobile whereas dimers and trimers move fast. Nitrogen-containing fragments are less strongly bound to the iron cluster and are therefore more mobile than carbon-only fragments with equal amount of atoms. On the iron nanoparticle surface, five-membered rings are formed first and then six-membered rings. The present simulations provide insight into the atomistic mechanisms involved in the nanocatalyzed synthesis of nitrogen-doped carbon nanotubes. The tendency of nitrogen atoms as parts of carbon fragments to repel the iron surface is confirmed by performing short molecular dynamics simulations at the density-functional theory level.
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