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.

NO Degradation on the Anatase TiO2 (001) Surface in the Presence of Water

“…Firstly, TD-DFTB in the frequency domain [27][28][29], which describes the response of a system to a perturbation within the linear response regime. Secondly, a real-time implementation [30], which allows for the propagation of electronic states in the time domain. In the following we refer to the two implementations as LR-DFTB (linear response-DFTB) and RT-DFTB (real time DFTB), respectively.…”

Plasmonic enhancement of molecular hydrogen dissociation on metallic magnesium nanoclusters

“…The 2020 release version of DFTB+ has been used 52,53 to simulate the electron dynamics associated with the plasmonic excitation and thus to obtain the optical absorption spectra and other related dynamics properties such as the hot-carrier distribution and the plasmonic lifetime. This is made possible with a new implementation to describe the electron dynamics based on timedependent SCC-DFTB (TD-SCC-DFTB).…”

“…This is made possible with a new implementation to describe the electron dynamics based on timedependent SCC-DFTB (TD-SCC-DFTB). 52,53 Within this theoretical framework, the electron dynamics is driven under the influence of an external time-varying potential (V ext (t)) or electric field (E(t))…”

“…Where H GS is the ground state Hamiltonian and µ is the dipole moment operator. 52,53 Two different kinds of external electric field have been used to drive the electron dynamics. For the optical absorption spectra, a Dirac δ pulse was used as external perturbation (E(t) = E 0 δ (t − t 0 )).…”

“…We present a comprehensive computational study of the electronic and optical properties of a set of metallic Mg nanoclusters and periodic Mg(0001) slabs based on density functional theory (DFT) and time-dependent density functional tight-binding (TD-DFTB) 52,53 calculations to simulate the optical absorption spectra and hot-electron distributions generated by incident light. We compare and contrast the optical properties of Mg with a conventional transition metal, namely Ag, before studying how hydrogen adsorption affects the plasmonic response of the nanoparticle.…”