Simulations of valence excited states in coordination complexes reached through hard X-ray scattering

Abstract

Theoretical guide to the valence electronic structure information that can be extracted from hard X-ray scattering experiments.

Predictions of Pre-edge Features in Time-Resolved Near-Edge X-ray Absorption Fine Structure Spectroscopy from Hole–Hole Tamm–Dancoff-Approximated Density Functional Theory

“…In the context of restricted active space second-order perturbation theory (RASPT2), both core and valence excitations can be treated with quantitative accuracy. Unfortunately, one is still limited by the computational cost of this approach. − Less computationally demanding single-reference methods, such as time-dependent density functional theory (TD-DFT), do not provide a satisfactory description of the nonadiabatic dynamics among the valence electronic states . State-specific methods, such as Δ self-consistent field (ΔSCF) , and restricted open-shell Kohn–Sham (ROKS), , may be more accurate than TD-DFT for core-excitation energies but fail to describe conical intersections between any pair of electronic states and are therefore unsuitable for applications to nonadiabatic dynamics.…”

The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

“…This approximation fails, e.g., for high-energy photons that have short wavelengths. In , this was originally addressed through a complete second-order multipole expansion, which was then applied to high-energy X-ray absorption and scattering processes. − However, the multipole expansion itself does not necessarily have a smooth convergence behavior toward the exact result, and is not origin independent unless using the correct length and velocity gauges. , In contrast, the plane-waveform of the wave vector, i.e., the exact semiclassical light–matter interaction operator, shows excellent stability also for small basis sets. ,− In , the operator has been implemented using the Gauss–Hermite quadrature, which makes it easy to implement both isotropic averages and defined directions of wave and polarization vectors. , This implementation has also been extended to circularly polarized light, allowing the computation of rotatory strengths and tensors beyond the dipole approximation …”

Sensitivity of Kβ mainline X-ray emission to structural dynamics in iron photosensitizer

“…K-edge X-ray emission simulations with RAS could previously only be performed for centrosymmetic complexes where excitations from s and p orbitals resulted in gerade and ungerade states respectively. 65,66 Here we use a projection operator, similar to the core-valence separation (CVS) technique, 67 to remove unwanted configurations with doubly occupied 1s and/or 3p orbitals. 68 Still, to ensure that the hole stays in the targeted orbitals, 1s and 3p orbitals were kept frozen in RASSCF optimizations.…”