Perspectives on the energy landscape of Au–Cl binary systems from the structural phase diagram of AuxCly (x + y = 20)

Ligand-protected gold (Au-L) nanoclusters have attracted much attention, where the reported electronic and geometric structures show great diversity. To give a direct and overall view of the energy landscape of Au-L binary systems, the AuxCly (x + y = 20) system is taken as a test case. By intensive global search of the potential energy surface at the level of density functional theory, a diverse set of global minima and low-lying isomers are found at each composition, and the structural phase diagram is obtained. The unbiased global search is carried out using the method combining the genetic algorithm with the TPSS functional. At x = 10 with the stoichiometric ratio of Au and Cl (1 : 1), the cluster presents a catenane structure. When x is in the range of 11–20, the clusters are Au-rich, and the Au–Cl system can be viewed as Cl-protected gold nanoclusters, where the gold cores consist of superatoms, superatom networks, or superatomic molecules in electronic structures. At x = 11–15, the gold cores consist of Au3, Au4 and Au5 2e-superatoms protected by staple motifs. At x = 16–20, the clusters are pyramidal superatomic molecules with one Au16 superatom core bonding with the four vertical atoms (Au or Cl). When x is in the scope of 9–5, the clusters are Cl-rich, and the 5d electrons of Au participate in bonding, resulting in high multiplicities. The Au–Cl binary system shows great diversity and flexibility in electronic and geometric structures, and there are corresponding structures to most of the experimentally produced Au-L nanoclusters in our structural phase diagram. We believe that the structural phase diagram gives an overall perspective on the universe of Au-L nanoclusters.