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 force field. We find a transition from cluster or molecular behavior below similar to 500 atoms to a mesoscale nanocrystal regime (well-defined bulk and surface properties) above similar to 750 atoms (2.7 nm). We find that the mesoscale nanocrystals melt via surface processes, leading to Tm,N=Tm,bulk - aN(-1/3), dropping from Tm,bulk, =1760 K to Tm,336=980 K. Cooling from the melt leads first to supercooled clusters with icosahedral local structure. For N > 400 the supercooled clusters transform to FCC grains, but smaller values of N lead to a glassy structure with substantial icosahedral character.
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