X-ray spectroscopies, by their high selectivity and sensitivity to the chemical environment around the atoms probed, provide significant insights into the electronic structures of molecules and materials. Interpreting experimental results requires reliable theoretical models, accounting for environmental, relativistic, electron correlation, and orbital relaxation effects in a balanced manner. In this work, we present a protocol for the simulation of core excited spectra with damped response timedependent density functional theory based on the Dirac−Coulomb Hamiltonian (4c-DR-TD-DFT), in which environmental effects are accounted for through the frozen density embedding (FDE) method. We showcase this approach for the uranium M 4 -and L 3edges and oxygen K-edge of the uranyl tetrachloride (UO 2 Cl 4 2− ) unit as found in a host Cs 2 UO 2 Cl 4 crystal. We have found that the 4c-DR-TD-DFT simulations yield excitation spectra that very closely match the experiment for the uranium M 4 -edge and the oxygen K-edge, with good agreement for the broad experimental spectra for the L 3 -edge. By decomposing the complex polarizability in terms of its components, we have been able to correlate our results with angle-resolved spectra. We have observed that for all edges, but in particular the uranium M 4 -edge, an embedded model in which the chloride ligands are replaced by an embedding potential reproduces rather well the spectral profile obtained for UO 2 Cl 4 2− . Our results underscore the importance of the equatorial ligands to simulating core spectra at both uranium and oxygen edges.
Synergistic effects of the electronic structure and morphology in the PTB7-Th polymer and the nonfullerene acceptor ITIC molecule resulted in state-of-art systems for organic solar cells, achieving over 12% power conversion efficiency (PCE) values. Furthermore, the substitution of harmful halogenated solvents to environmentally friendly solvents that do not compromise PCE values has become a subject of great interest in recent literature. In this work, we employed sulfur K-edge Angle-Resolved Near-Edge X-ray Absorption Fine Structure, Resonant Auger Spectroscopy, and the core-hole clock spectroscopy in an attempt to gain information on the effect of different processing methods on the electronic and morphological properties of these systems. Comparison with the PTB7-Th:PCBM blend, which uses a conventional acceptor molecule, was also performed. Steady-state and time-resolved photoluminescence results were obtained for neat PTB7-Th and blends with ITIC and PCBM. Theoretical calculations were performed utilizing restricted-excitation-window time-dependent density functional theory. Our results shows that ortho-methylanisole is a potential replacement to the conventional halogenated solvent ortho-dichlorobenzene, as they show that in terms of morphology and charge transfer dynamics, no expressive changes occurred by varying the solvent and by thermal annealing.
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