Deciphering the structural code for the face-centered-cubic ligand protected intermetallic AuAg nanoclusters

The incorporation of Ag atoms into ligand-protected gold nanoclusters is an effective way to tune their properties for applications in optics, electronics, and catalysis. However, the precise identification of preferred doping sites is challenging owing to its high structural complexity, which hinders establishing the structure-activity relationship. Here, through density functional theory calculations coupled with energy evaluation, delicate structural analysis, valence electron counting, and localized molecular orbital topology, we characterize the tetrahedral Au3Ag with closed-shell two valence electrons [Au3Ag(2e)] as a fundamental building block in face-centered-cubic (FCC) ligand-protected AuAg (LP-AuAg) alloy nanoclusters. The kernel structures of FCC LP-AuAg alloy clusters are constructed by rational spatial packing of Au3Ag(2e), Au4(2e), and Au3(2e) blocks, aligning with the grand unified model of ligand-protected Au nanoclusters. In addition, we predict 40 FCC LP-AuAg alloy nanoclusters with 141 low-energy isomers. This work underscores the crucial role of subset blocks in stabilizing the entire cluster and provides valuable insights into the structural features of FCC LP-AuAg alloy clusters.