Single-Atom-Intermediated Raman Activation (SAIRA) Mechanism on Pyridine-Adsorbed Au/g-C3N4 and Periodic Trends from a 30 d-Block Element Screening

Surface-enhanced Raman scattering (SERS) on single-atom platforms offers a reproducible, hotspot-free sensing paradigm, yet its fundamental mechanism remains elusive. Herein, we present a comprehensive density functional theory (DFT) investigation into the “Single-Atom-Intermediated Raman Activation (SAIRA)” mechanism using a pyridine-adsorbed Au/g-C3N4 model. Ground-state electronic structure analyses reveal that the cavity-confined Au single atom acts as an indispensable polarization center that triggers strong orbital hybridization and interfacial charge transfer upon molecular adsorption. Consequently, the simulated static Raman activity yields a chemical enhancement factor about 1 order of magnitude higher than that of conventional Au20 clusters. Based on a model chemistry established through systematic benchmark evaluations of DFT functionals and basis sets, this protocol successfully captured experimental observations across various probe molecules. Importantly, extending this validated protocol to a two-dimensional descriptor map based on energetic and electronic parameters for 30 d-block elements reveals that the systems segregate into three distinct mechanistic domains, exhibiting pronounced interdomain variations in Raman enhancement. Furthermore, this 2D descriptor mapping demonstrates high robustness against alternative model chemistries. Ultimately, this work establishes electronic-level design principles not only for next-generation single-atom-based SERS technologies but also for the rational design of functional single-atom catalysts.