Evolution of Electronic Structure of Cuboid Thiolate-Monolayer-Protected Gold Nanocrystals

The exploration of the boundary between nonmetallic state and the metallic state of metal clusters is an interesting topic. However, due to the difficulty in obtaining the crystal structure of large-sized atomically accurate metal clusters, it is still very difficult to determine the critical size to transition from a nonmetallic state to a metallic state. In this study, the evolution of electronic structure and the optical absorption property of a series of thiolate (SR) monolayer-protected gold clusters with a cuboid n × m × l packing of kernel gold atoms is studied. The density functional theory (DFT) calculation results show that the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap of cuboid gold nanocrystals decay very slowly with the increase in size. By studying the shape evolution of the optical absorption curve, the critical size of the transition from nonmetallic state to metallic state is preliminarily determined. Au 264 (SH) 96 is determined to be a critical size for the transition from nonmetallic to metallic state in the cuboid gold nanocrystals.