Implementation of velocity-gauge RT-TDDFTB Ehrenfest dynamics*

Length-gauge real-time time-dependent density functional tight-binding (LG-RT-TDDFTB) has been widely used to probe light-matter interactions for non-periodic systems. However, the translational symmetry of the Hamiltonian is broken by the external electric field in this gauge and cannot be used for periodic systems. Recently, we derived a new velocity-gauge real-time time-dependent density functional tight-binding (VG-RT-TDDFTB) formalism for probing electron dynamics in large, condensed matter systems within periodic boundary conditions. Furthermore, we extended VG-RT-TDDFTB to the semiclassical Ehrenfest method, making our approach accessible for probing ultrafast electron-nuclear dynamics for complex systems. Our implementation uses a hybrid MPI/OpenMP parallelization scheme for massive parallelization to treat large systems on multi-core supercomputers. Our calculations demonstrate that the approach enables large electron dynamics for periodic systems containing thousands of atoms on a modest computer cluster.