Snapshots from a computer simulation of the freezing of a silver nanodroplet. The nanodroplet, made of several hundred atoms, starts in the liquid state at high temperature (left picture). Upon cooling down, the nanodroplet solidifies as a face centered cubic nanoparticle with a stacking fault (right picture).
 

Snapshots from a computer simulation of the growth of a nanoparticle composed by C₆₀ molecules (each sphere is a molecule). Starting from a low-symmetry structure (left picture), newly added molecules cause the formation of a highly symmetric cluster of decahedral structure (right picture), with symmetric islands on its top (molecules in the islands are depicted in yellow). Decahedral structures are non-cystalline. They cannot be found in bulk solids, but they are frequently formed in nanoclusters. This is an example of the much wider structural variety of nanoparticles with respect to bulk matter.
 

Typical behavior of the structural transitions from icosahedral to decahedral to face-centered-cubic structures with increasing size N. The latter are crystalline structures, which resemble pieces of bulk crystal, while icosahedra and decahedra cannot be found in bulk crystals. As size increases, the most favorable structures (identified by the lowest excess energy ?) pass from the quasi-spherical but highly strained icosahedra, to the less compact but less strained decahedra and finally to crystalline clusters, which are not strained but far from a spherical shape. Transition sizes from icosahedra to decahedra and from decahedra to crystalline structures are indicated.