Microscopic mechanisms of the growth of metastable silver icosahedra

The growth of free silver nanoclusters is investigated by molecular-dynamics simulations up to sizes close to N = 600 atoms on realistic time scales, and in a temperature range from 400 to 650 K. At low and intermediate temperatures, we grow mainly noncrystalline structures, as icosahedra and decahedra. In particular, at N > 200, we obtain that perfectly ordered metastable icosahedra are very likely grown: either by a shell-by-shell mode on a small-size stable icosahedron, or by a complete structural transformation from a decahedron to a metastable icosahedron. The latter mechanism can explain why large silver icosahedra are more abundant than large decahedra in experiments. At high temperatures, crystalline fcc clusters are very frequently grown.