Prediction of the AuS crystal via a superatom network model: from clusters to solids.

Owing to their unique properties, thiolate-protected gold clusters (denoted as Au(SR)) have attracted intense research interest both experimentally and theoretically. The superatom complex (SAC) and superatom network (SAN) models are significantly well-known concepts to explain the electronic stability of Au(SR). Based on the structural characters of Au(SR), the tetrahedral Au unit was found to be an elementary building block and used to design a series of tetrahedron-network clusters. In this work, we first build a Au(μ-S)(SH) cluster consisting of a network of four non-conjugated tetrahedral Au units and confirm that it is a local minimum on the potential energy surface by density functional theory calculations. Chemical bonding analysis by the AdNDP method reveals that the electronic structure of Au(μ-S)(SH) follows the SAN (4 × 2e) model. Based on the structural character of the Au(μ-S)(SH) cluster, we utilize the diamond lattice as a template to construct a stable AuS crystal in which each S atom binds to four Au superatoms. The computational results demonstrate that the structure has rather good dynamic and thermal stabilities, and it is an indirect semiconductor with a band gap of 2.68 eV at the HSE06 level. Chemical bonding analysis performed by the SSAdNDP method reveals that the AuS can be seen as a SAN crystal. These bonding patterns and properties of the solid provide references for further investigation of cluster-assembled materials.