Photoinduced Charge Transfer versus Fragmentation Pathways in Lanthanum Cyclopentadienyl Complexes

Abstract

This study compares two competing pathways of photoexcitations in gas-phase metal−organic complexes: first, a sequence of phonon-assisted electronic transitions leading to dissipation of the energy of photoexcitations and, second, a sequence of light-driven electronic transitions leading to photolysis. Phonon-assisted charge carrier dynamics is investigated by combination of the density matrix formalism and on-the-fly nonadiabatic couplings. Light-driven fragmentation is modeled by a time-dependent excited-state molecular-dynamics (TDESMD) algorithm based on Rabi theory and principles similar to the trajectory surface hopping approximation. Numerical results indicate that, under the medium intensity of the laser field, lightdriven electronic transitions are more probable than phonon-assisted ones. The formation of multiple products is observed in TDESMD trajectories. Simulated mass spectra are extracted from TDESMD simulations and compared to experimental photoionization time-of-flight (PI-TOF) mass spectra. It is found that several features in the experimental mass spectra are reproduced by the simulations.

Unraveling Photodimerization of Cyclohexasilane from Molecular Dynamics Studies

“…Experimentally, both excimer lasers with a wavelength of 308 nm and HgXe lamps with UV irradiation have been used for the initiation of CHS photopolymerization. , The initial excitation energies in the TDESMD calculations, chosen based on the oscillator strengths of the optical transitions, are in the range of 5.5 to 5.8 eV, with a corresponding wavelength of 225–214 nm. The initial conditions in the simulation are in qualitative agreement with experimental processing conditions, where excitation is initiated slightly above the band gap. , The formalism underlying TDESMD calculations has been described in detail elsewhere . Here the technical details of this work are available in the Supporting Information.…”

“…In our previous study, density-functional-theory (DFT)-based time-dependent excited-state molecular dynamics (TDESMD) was used to investigate the photochemistry of small organic molecules , and large metal–organic complexes. − The atomic models were isolated in the gas phase such that the photochemistry should be interpreted as unimolecular reactions. The photochemical processes were mainly characterized as photodissociation, even though minor photoisomerization events were observed for certain fragments in simulations based on organic molecules. , In this work, we perform TDESMD calculations on a pair of CHS monomers in the gas phase to simulate photoinduced reactions.…”

Hot Carrier Dynamics at Ligated Silicon(111) Surfaces: A Computational Study

“…Representative examples using high-temperature AIMD to model chemical reactions are available in previous work. − The other one at ambient temperature serves as a foundation for computing nonadiabatic couplings and elements of the Redfield tensor, which describes excited-state dissipative dynamics of charge carriers. The methodologies for computing charge carrier dynamics can be found elsewhere. − All calculations are performed using periodic plane wave DFT within the Vienna Ab Initio Simulation Package (VASP). − The projected augmented wave (PAW) potentials and the generalized gradient approximation (GGA) , with Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional are adopted for the calculations. The long-range internuclear interactions are treated with the semiempirical pairwise corrections (DFT+D2) .…”

Nonradiative Relaxation Dynamics of a Cesium Lead Halide Perovskite Photovoltaic Architecture: Effect of External Electric Fields

“…Figure a shows the absorption spectra for the thin film under various external electric field strengths. The absorption spectra are obtained by adopting independent orbital approximations (IOAs) − for the calculation of oscillator strengths, which are then broadened with a factor of 0.1 eV representing thermal and inhomogeneous broadening. The absorption spectra in the high-intensity region are associated with optical transitions within the perovskite slab.…”