The smallest triple-ring tubular gold clusters M₂@Au₁₅ with M = Mo, W: stability, electronic properties and nonlinear...

The smallest triple ring tube-like gold clusters M₂@Au₁₅ with M = Mo, W and q = 1, 0, -1 are reported for the first time. Incorporation of an M₂ dimer results in a remarkable modification of both atomic and electronic structures of the gold host. While the bare Au₁₅ cluster exhibits a 3D cage shape, the doubly doped clusters M₂@Au₁₅ in all charge states are found to prefer a tubular form composed of three five-membered Au rings in an anti-prism arrangement and stabilized by an M₂ unit placed inside the tube-like Au₁₅ gold framework. The equilibrium geometry of both M₂@Au₁₅ and M₂@Au₁₅^- is not much modified upon electron detachment from or attachment to their pure gold counterpart. The anion M₂@Au₁₅^- with 28 itinerant electrons establishes an electron shell configuration of 1S²1P⁶1D¹⁰2S²1F⁸, in which the 1F shell splits into four different sub-levels. These stable clusters are thus not magic. Computed results on the first and second hyper-polarizability parameters of the doped clusters show a strong dependence on the charge. Overall, the neutral M₂@Au₁₅ is found to exhibit a particularly strong nonlinear optical (NLO) response. These clusters can also be extended to 1D nanowires, providing helpful guidance for the design of novel gold-based nanowires with rich optoelectronic properties.