Hydration Accelerates Radiative and Nonradiative Recombination in Small TiO₂ Nanoclusters

We report a nonadiabatic molecular dynamics (NA-MD) study on radiative and nonradiative recombination dynamics in small bare and hydrated titania nanoclusters, (TiO₂)₄(H₂O)_m (m = 0, 2, 4) and (TiO₂)₈(H₂O)_m (m = 0, 2, 5). Our findings indicate that increased hydration raises excitation energies and nonadiabatic couplings, accelerating both radiative and nonradiative recombination. We test the robustness of this predicted trend with respect to several important choices in our NA-MD methodology. We find that nuclear trajectories from classical force fields closely match those from density functional theory (DFT) calculations, with recombination time scales weakly dependent on the choice of pure or hybrid functionals. Additionally, decoherence corrections yield longer nonradiative recombination times than the overcoherent fewest switches algorithm. Overall, our predicted hydration-induced recombination acceleration in titania nanoclusters is found to be independent of the main choices in our NA-MD approach, thus giving us confidence in our results.