Modulation of Third-Order Nonlinear Optical Response in Copper-Induced Gold Nanoclusters

Nonlinear optical (NLO) materials play a pivotal role in controlling laser characteristics, including phase and frequency, making them essential for optoelectronic applications. This study presents a quantum chemical investigation into the effects of copper doping on the NLO properties of small gold clusters. Using density functional theory with the CAM-B3LYP/LanL2DZ level of theory, we examined both pure (Au_m, where 8 ≤ m ≤ 10) and copper-doped (Au_m-xCu_x) gold clusters. To the best of our knowledge, no theoretical studies have been reported on the nonlinear optical properties of pure and Cu-doped clusters. Copper incorporation leads to a marked reduction in the HOMO-LUMO energy gap from 4.77 eV down to 1.59 indicating enhanced NLO response. The dynamic NLO properties were computed at a standard Nd:YAG laser wavelength (1064 nm; ω = 0.0428 au). Among the doped clusters, Au₁Cu₈ exhibited the highest first hyperpolarizability β_(-ω,ω,0), reaching 5.27 × 10⁶ au. The second hyperpolarizability γ_(-ω;ω,0,0) peaked at 3.89 × 10⁷ au for Au₄Cu₅, while the third-order response γ_(-ω;ω,0,0) was highest for Au₂Cu₈ at 1.03 × 10¹⁰ au. These results highlight copper-doped gold clusters as promising candidates for the development of high-performance NLO materials, with potential applications in next-generation electronic and photonic devices.