Plasmons and Excitons in Pd-Doped Ag Nanoparticles from an Ab Initio GW-BSE Approach

Combining transition-metal catalyst materials with plasmonic metals can enhance photocatalytic reaction rates, selectivity, and open non-equilibrium reaction paths. These effects are initiated by surface plasmon resonances (SPRs) in the plasmonic metal, and direct electron-hole (e-h) interactions can also significantly alter the landscape of excited states and affect SPR evolution. However, <i>ab initio</i> calculations in realistic nanoparticle systems have mostly either neglected e-h interactions or been limited to very small (&lt;35 atom) clusters that display zero-dimensional-like excitation spectrum due to strong confinement effects and fail to describe plasmons due to use of the Tamm-Dancoff approximation (TDA). Here, we study Pd-doped Ag nanoparticles of up to 147 atoms with varying dopant levels, including e-h interactions and e-h recombination terms that are not present in the TDA, through the first-principles GW plus Bethe-Salpeter equation (BSE) approach. Applying new low-rank approximations and spectral folding techniques to accelerate these calculations, we can directly obtain excited states of nanoparticles capturing both plasmonic and excitonic effects. For small systems, we observe strong e-h interactions that redshift the spectrum by up to ~2 eV, demonstrating the importance of excitonic effects for spatially confined metallic systems. We also analyze the excitonic and plasmonic character of the excitations as a function of size and doping, and the impact of many-body interactions for reactions involving excited-state potential-energy surfaces.