Atomistic simulation for the size-dependent melting behaviour of vanadium nanowires

Molecular dynamics and the modified analytical embedded atom potential are employed to study the size effect of a V nanowire (NW) on the melting behaviour. It is found that the melting temperature of the NW and its latent heat of fusion are much lower than those of the bulk, and depend strongly on the size. The calculated self-diffusion coefficient indicates that the premelting phenomenon first occurs at the surface and then spreads inwards with increasing temperature. The activation energy Q of the shell decreases as the reciprocal of the diameter increases. The lower activation energy indicates that premelting and melting can take place more easily. Finally, some representative snapshots on the temperature dependence of the cross-section atomic structure reveal that the melting mechanism of a large-sized NW is quite different from that of a small-sized one. For large-sized NWs (>4.0 nm), the surface plays a dominant role in the melting process, which is made up of two stages, i.e. gradual premelting and rapid melting. For small-sized NWs (<3.0 nm), the melting results mainly from the anharmonic effect of crystal lattice vibration, and the surface melting is barely noticeable. When the diameter size of the NWs ranges from 3.0 to 4.0 nm, both foregoing factors have an influence on the melting behaviour, which indicates that the critical diameter of the NW with a different melting mechanism is about 3.0 nm.