Quantum dynamics simulations: combining path integral nuclear dynamics and real-time TDDFT

We report a practical computational scheme for quantum electron-nuclear dynamic simulations, applicable to both finite (e.g. ozone) and periodic systems (e.g. graphene), using a combination of real-time time dependent density functional theory (rt-TDDFT) and ring polymer molecular dynamics. This scheme could deal with quantum effects of nuclei beyond Ehrenfest dynamics in TDDFT simulations. We find that when nuclear quantum effects (NQEs) are taken into account, the atomic structure of ozone splits into normal states and cyclic states upon photoexcitation. NQEs broaden the electronic density of states and induce strong orbital couplings, leading to new nuclear trajectories and carrier dynamics different from classical simulations. We also observe a charge carrier redistribution accelerated by the quantum motions of carbon atoms in graphene, yielding an exponential decay with fast relaxation time. These developments and practices represent an advance in studying full quantum dynamics of electrons and nuclei from first-principles, towards a complete and predictive understanding of quantum interactions and dynamics in large molecules and complex materials at the microscopic level.