  In this study, the melting and coalescence of Au nanoparticles were
investigated using molecular dynamics simulation. The melting points of
nanoparticles were calculated by studying the potential energy and Lindemann
indices as a function of temperature. The simulations show that coalescence of
two Au nanoparticles of the same size occurs at far lower temperatures than
their corresponding melting temperature. For smaller nanoparticles, the
difference between melting and coalescence temperature increases. Detailed
analyses of the Lindemann indices and potential energy distribution across the
nanoparticles show that the surface melting in nanoparticles begins at several
hundred degrees below the melting point. This suggests that the coalescence is
governed by the liquid-phase surface diffusion. Furthermore, the surface
reduction during the coalescence accelerates its kinetics. It is found that for
small enough particles and/or at elevated temperatures, the heat released due
to the surface reduction result in a melting transition of the two attached
nanoparticles.
