Prediction of the Au4S crystal via a superatom network model: from clusters to solids

Owing to their unique properties, thiolate-protected gold clusters (denoted as Aun(SR)m) 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 Aun(SR)m. Based on the structural characters of Aun(SR)m, the tetrahedral Au4 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 Au22(μ4-S)(SH)12 cluster consisting of a network of four non-conjugated tetrahedral Au4 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 Au22(μ4-S)(SH)12 follows the SAN (4 × 2e) model. Based on the structural character of the Au22(μ4-S)(SH)12 cluster, we utilize the diamond lattice as a template to construct a stable Au4S crystal in which each S atom binds to four Au4 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 Au4S can be seen as a SAN crystal. These bonding patterns and properties of the solid provide references for further investigation of cluster-assembled materials.