Photoexcited Polaron Dynamics in Rutile TiO₂ from First-Principles On-the-Fly Surface Hopping

Photoinduced polaron dynamics challenges the classical path approximation (CPA), which prescribes nuclear motion on a single potential-energy surface (PES). To overcome this limitation, we use ΔSCF-based on-the-fly surface hopping involving both ground- and excited-state PESs to study photoexcited polaron dynamics in rutile TiO₂. The simulations capture electron and hole polaron formation, migration, recombination, and subsequent ultrafast lattice relaxation. The electron-hole recombination lifetime increases by approximately two orders of magnitude relative to CPA-NAMD, from 38 ps to 6.3 ns. This increase arises from reduced nonadiabatic coupling: excitation-induced electron redistribution substantially changes the orbitals relative to the ground state at the same nuclear geometry. These results highlight the importance of orbitals associated with both PESs and lattice feedback in electron-hole recombination. The approach provides a tool for investigating excited-state dynamics in solids where the CPA breaks down.