A real-time time-dependent density functional tight-binding implementation for semiclassical excited state electron-nuclear dynamics and pump-probe spectroscopy simulations

Abstract

The increasing need to simulate the dynamics of photoexcited molecular and nanosystems in the sub-picosecond regime demands new efficient tools able to describe the quantum nature of matter at a low computational cost. By combining the power of the approximate DFTB method with the semiclassical Ehrenfest method for nuclearelectron dynamics we have achieved a real-time time-dependent DFTB (TD-DFTB) implementation that fits such requierements. In addition to enabling the study of nuclear motion effects in photoinduced charge transfer processes, our code adds novel features to the realm of static and time-resolved computational spectroscopies. In particular, the optical properties of periodic materials such as graphene nanoribbons or the use of corrections such as the "LDA+U" and "pseudo SIC" methods to improve the optical properties in some systems, can now be handled at the TD-DFTB level.Moreover, the simulation of fully-atomistic time-resolved transient absorption spectra and impulsive vibrational spectra can now be achieved within reasonable computing time, owing to the good performance of the implementation and a parallel simulation protocol. Its application to the study of UV/visible light-induced vibrational coherences in molecules is demonstrated and opens a new door into the mechanisms of non-equilibrium ultrafast phenomena in countless materials with relevant applications.

Interplay between Intra- and Interband Transitions Associated with the Plasmon-Induced Hot Carrier Generation Process in Silver and Gold Nanoclusters

“…This EOM is nonlinear because the Hamiltonian depends on the density matrix via self-consistent terms and includes the same physics, albeit approximately, as the full TD-DFT scheme. For details on the theoretical method and its computational implementation, we refer the readers to Bonafeé t al., 48 where a link to download the DFTB+ version employed to perform the calculations presented here is provided. Dirac delta pulses and sinusoidal time-dependent electric fields have been used as external electric fields to perturb the whole system and obtain different dynamical information such as optical absorption spectra and whole electron dynamics associated with the plasmon-induced hot electron generation process for both metals.…”