Size-dependent melting and coalescence of tungsten nanoclusters via molecular dynamics simulation.

We obtained the melting temperatures of the W nanoclusters with diameters in the range of 2.5-5.0 nm which manifest the good linear fitting to the size of nanoclusters (N(-1/3)). Four different initial configurations at each size produce nearly the same melting points, with the maximum discrepancies less than 40 K. The extrapolated bulk melting point 4210 K is lower than the simulated bulk value 4520 K. Surface premelting is detected by density profiles, deformation parameters and bond orientational order parameters. Moreover, by dividing particles into surface and subsurface layers, we analyzed the different behaviors of the inner and outer shell atoms during melting in detail. During coalescence of W nanoclusters (W(N) + W(N)→ W(2N)), the shape change is along the path of peanut → rod-like → spherical → liquid structure. The obtained melting points from W(2N) are in good agreement with those from W(N) + W(N), indicating that melting temperatures are mainly relevant to the number of atoms, and nearly not affected by the different surface areas in nanoclusters.