Ultrafast Nonadiabatic Electron Relaxation Dynamics in Photoexcited C₆₀ Molecules

Fullerene molecules, being attractive for fundamental research and key building blocks in materials of energy harvesting, are important for ultrafast electron transfer studies. The nonradiative electron-relaxation dynamics in a C₆₀ molecule is investigated after chosen initial photoexcitations. The methodology includes nonadiabatic molecular simulation combined with time-dependent density functional theory and a semiclassical surface hopping approach. Results treating the exchange-correlation by using hybrid functionals, Becke three-parameter Lee-Yang-Parr (B3LYP) and Perdew-Burke-Ernzerhof (PBE0), are presented. Both approaches produce similar unoccupied band structures in the ground state that qualitatively agree with our many-electron excited state calculation. The model-dependent differences in the ultrafast population dynamics, including the transient entrapment of the population, are studied systematically. The trend of the results demonstrates a universal dependence on the structure of the unoccupied band offering a spectroscopic route to probe the structure. Predictions can be assessed by comparison with ultrafast transient absorption or time-resolved photoelectron spectroscopy measurements. By selectively comparing with inexpensive nonempirical PBE results, the study facilitates method optimization for future studies of technologically important and larger fullerene complexes.