Melting and crystallization in Ni nanoclusters: The mesoscale regime

We studied melting and freezing of Ni nanoclusters with up to 8007 atoms (5 .7 nm) using molecular dynamics with the quantum-Sutten-Chen many-body forc e field. We find a transition from cluster or molecular behavior below simi lar to 500 atoms to a mesoscale nanocrystal regime (well-defined bulk and s urface properties) above similar to 750 atoms (2.7 nm). We find that the me soscale nanocrystals melt via surface processes, leading to T-m,T-N=T-m,T-b ulk-alphaN(-1/3), dropping from T-m,T-bulk=1760 K to T-m,T-336=980 K. Cooli ng from the melt leads first to supercooled clusters with icosahedral local structure. For N > 400 the supercooled clusters transform to FCC grains, b ut smaller values of N lead to a glassy structure with substantial icosahed ral character. (C) 2001 American Institute of Physics.