Tracking holes and their reactivity in photon-driven reactions using Real-Time Time-Dependent Density Functional Theory (RT-TDDFT)*

Photocatalytic reactions on semiconductor surfaces that produce hydrogen have the potential of addressing our growing energy needs. However, the possible reaction intermediates and trajectories associated with such photon-driven reactions are currently not well understood. Our aim is to study the response of molecular systems upon photoexcitation. We are particularly interested in the evolution of a system on the excited-state potential energy surface and the interaction of the molecular intermediates with its surroundings after excitation which leads to the desired reaction. We use ab initio nonadiabatic simulations to study the time evolution of photoexcited states, and we simulate the coupled electron-ion dynamics using RT-TDDFT-based Ehrenfest dynamics. This is a promising nonadiabatic dynamics scheme given the considerable sizes of the molecular systems of interest. We compare the ultrafast dynamics of the ``photogenerated-hole'' as captured by RT-TDDFT Ehrenfest dynamics with the commonly used Born-Oppenheimer dynamics at similar time scales and identify the key physical characteristics that differentiate one from the other, thereby empirically testing a more computationally intensive nonadiabatic scheme for elucidating the physics of photoexcited systems.