Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

Carbon family elements (Si, Ge, Sn, Pb) have attracted a lot of attention because of their unique structural features and potential applications in microelectronics industry. Here, the structure, chemical stability, electronic properties, and nonlinear optical properties of neutral and charged Au@X20H20 (X= Si, Ge, Sn, Pb) clusters have been systematically studied using densityfunctional theory calculations. Structurally, the neutral/anionic Au@X20H20 (X= Si, Ge, Sn) as well as cationic Au@Pb20H20 possess Au-endohedral (XH) 20 unit, forming fullerene-like framework, whereas other species are Au-doped structures with hydrogen-bridged bond. Analysis of binding energy and HOMO-LUMO energy gaps reveals that the charged clusters possess high chemical stabilities due to closed-shell structures. The charge transfers from X-20 cage to Au atom, and the Au atom acts as electron acceptor. The Au atom and charged states play an important role in the structural stability, and can effectively modulate the electronic properties of clusters. Interestingly, the neutral Au@X20H20 (X= Si, Sn) clusters possess large first hyperpolarizabilities, especially for Au@Sn20H20, which has remarkably giant value (similar to 5.65x10(8) a. u.), and the enhanced NLO behaviors can be further explained by the TDDFT calculation. The work may provide a theoretical reference for further applications considered as novel cluster-assembled nanomaterials.