Nonradiative Dynamics of [Au₂₅(SCH₃)₁₈]^- Nanoclusters: Many-Body versus Single-Particle Excited State Dynamics

Thiolate-protected gold nanoclusters (Au NCs) have attracted significant attention for their potential in photovoltaics, photocatalysis, and photoluminescence. Realizing the full potential of these applications requires a detailed understanding of the photoinduced excited-state dynamics. Here, we investigate the nonradiative relaxation dynamics of photoexcited carriers in the prototypical [Au₂₅(SCH₃)₁₈]^- nanocluster using ab initio nonadiabatic molecular dynamics (NAMD) simulations, incorporating both single-particle (SP) and many-body (MB) treatments of electronic excited states. Our results reveal distinct and contrasting roles of MB effects in internal conversion and nonradiative recombination processes. In particular, MB effects accelerate the relaxation of high energy excited states to the subpicosecond time scale by enhancing nonadiabatic couplings relative to SP description. In contrast, MB treatment slows the electron-hole recombination of the lowest-lying excited states (431.8 ps vs 136.5 ps in SP), owing to the weakened nonadiabatic couplings with ground state and enhanced uphill transitions among degenerate lowest-lying excited states. Relaxation from higher-energy states involves both core-to-semiring and core-to-core transitions, whereas charge recombination predominantly proceeds via core-to-core pathways. Low-frequency vibrational modes associated with the Au(core)-Au(core) and Au(core)-Au(ring) interactions couple strongly to the nonradiative relaxation processes. Overall, inclusion of MB effects in NAMD simulations yields relaxation time scales better agreement with experiments. These findings highlight the importance of MB effects in modeling excited state dynamics of Au NCs and provide fundamental insights into relevant to their application in optoelectronic energy conversion devices.