text: Bulk gold exhibits a face-centered cubic (fcc) structure. As gold particle size decreases the fcc structure of gold transforms into a centered-icosahedral structure illustrated by . It can be shown that the fcc structure can be extended by a half unit cell in order to make it look like a cuboctahedral structure. The cuboctahedral structure maintains the cubic-closed pack and symmetry of fcc. This can be thought of as redefining the unit cell into a more complicated cell. Each edge of the cuboctahedron represents a peripheral Au–Au bond. The cuboctahedron has 24 edges while the icosahedron has 30 edges; the transition from cuboctahedron to icosahedron is favored since the increase in bonds contributes to the overall stability of the icosahedron structure.
  The centered icosahedral cluster  is the basis of constructing large gold nanoclusters.  is the endpoint of atom-by-atom growth. In other words, starting with one gold atom up to , each successful cluster is created by adding one additional atom.  The icosahedral motif is found in many gold clusters through vertex sharing ( and ), face-fusion ( and ), and interpenetrating biicosahedrons (, , , and ). Large gold nanoclusters can essentially be reduced to a series of icosahedrons connecting, overlapping, and/or surrounding each other. The crystallization process of gold nanoclusters involves the formation of surface segments that grow towards the center of the cluster. The cluster assumes an icosahedral structure because of the associated surface energy reduction.