Probing electron-nuclear dynamics of large systems using velocity-gauge real-time time-dependent density functional tight binding

Excited-state electron-nuclear simulations using time-dependent density functional theory can probe time-resolved dynamics in ultrafast phenomena; however, its high computational cost poses a severe challenge to simulating the large, complex systems in current experiments. In this work, we present a new, efficient excited-state electron-nuclear dynamics approach based on velocity-gauge real-time time-dependent density functional tight binding. Using this approach, we carried out excited-state electron-nuclear dynamics simulations of nanoscale systems for several picoseconds, enabling us to capture various time-resolved ultrafast processes, including excited electron-hole generation/transfer and nonradiative recombination. These simulations are completely beyond the scope of traditional adiabatic molecular dynamics simulations or conventional time-dependent density functional theory. When applied to large, solvated systems, we observe that the presence of water significantly increases the electron-hole recombination time in fullerene, revealing a clear and intuitive physical picture of the generation/diffusion of hole traps in individual water molecules. Our approach presents a new capability for simulating ultrafast, excited-state electron-nuclear dynamics in large systems, providing time-resolved mechanistic insight into their ultrafast processes.