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

Abstract

Time-resolved near-edge X-ray absorption fine structure (TR-NEXAFS) spectroscopy is a powerful technique for studying photochemical reaction dynamics with femtosecond time resolution. In order to avoid ambiguity in TR-NEXAFS spectra from nonadiabatic dynamics simulations, core-and valence-excited states must be evaluated on equal footing and those valence states must also define the potential energy surfaces used in the nonadiabatic dynamics simulation. In this work, we demonstrate that hole−hole Tamm− Dancoff-approximated density functional theory (hh-TDA) is capable of directly simulating TR-NEXAFS spectroscopies. We apply hh-TDA to the excited-state dynamics of acrolein. We identify two pre-edge features in the oxygen K-edge TR-NEXAFS spectrum associated with the S 2 (ππ*) and S 1 (nπ*) excited states. We show that these features can be used to follow the internal conversion dynamics between the lowest three electronic states of acrolein. Due to the low, O(N 2 ) apparent computational complexity of hh-TDA and our GPU-accelerated implementation, this method is promising for the simulation of pre-edge features in TR-NEXAFS spectra of large molecules and molecules in the condensed phase.

Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory for Accurate X-ray Absorption Spectroscopy

“…Alike shifts are also needed with TDDFT variants for X-ray spectroscopy, like the recently developed hole-hole Tamm-Dancoff-approximated density functional theory (hh-TDA). 19 These large shifts are attributed to the lack of description of core-hole orbital relaxation effects in the approximate exchange-correlation functionals used in TDDFT, that cannot account for the drastic change in the Coulomb interaction of the remaining electrons when a core electron is excited. A simple remedy to orbital relaxation is not available in the context of TDDFT approach, despite some attempts on applying linear response on a set of orbitals converged for a core-hole (CH) excited state, which improves the description of XAS.…”

“…Still, the accuracy of TDDFT to predict experimental X-ray states is very crude, with errors as large as ∼10 eV for second period elements like C, N, O, and F and even larger errors for heavier elements. Alike shifts are also needed with TDDFT variants for X-ray spectroscopy, like the recently developed hole–hole Tamm–Dancoff-approximated DFT (hh–TDA) and orthogonality constrained DFT (OCDFT) . These large shifts are attributed to the lack of description of core-hole orbital relaxation effects in the approximate exchange–correlation functionals used in TDDFT, which cannot account for the drastic change in the Coulomb interaction of the remaining electrons when a core electron is excited.…”

Generalization of One-Center Nonorthogonal Configuration Interaction Singles to Open-Shell Singlet Reference States: Theory and Application to Valence-Core Pump-Probe States in Acetylacetone

“…Two DFT-based methods proposed in the last two years explore unusual response approaches to capture both c → SOMO transitions. The first is the hole–hole Tamm-Dancoff Approximated (hh-TDA) DFT, which shows promise in its efficiency yet still suffers from a lack of orbital relaxation and the difficulties associated with converging a doubly electron-attached reference . In contrast, mixed-reference spin-flip (MR-SF)-TDDFT employs both M s = 1 and −1 open-shell core excited triplet references, relaxed accordingly, to access both the valence excited singlet state and the c → SOMO configurations via spin-flip operations …”

Deciphering Methylation Effects on S2(ππ*) Internal Conversion in the Simplest Linear α,β-Unsaturated Carbonyl

“…Experimentally, photoexcitation (∼193 nm) to the S 2 state of AC has predominantly been pursued to investigate photodissociation and photofragment formation. ,− However, the photochemical details of the internal conversion dynamics following S 2 photoexcitation and the characterization of the conical intersections for nonradiative relaxation have received much less attention. Recently, nonadiabatic ab initio multiple spawning (AIMS) simulations (employing hole–hole Tamm–Dancoff-approximated ( hh -TDA) density functional theory − ) have been performed for AC initiated from the S 2 excited state for the prediction of the time-resolved near-edge X-ray absorption fine structure spectrum . However, the underlying mechanistic details have not been discussed.…”

“…Recently, nonadiabatic ab initio multiple spawning (AIMS) simulations 66 (employing hole–hole Tamm–Dancoff-approximated ( hh -TDA) density functional theory 67 − 70 ) have been performed for AC initiated from the S 2 excited state for the prediction of the time-resolved near-edge X-ray absorption fine structure spectrum. 71 However, the underlying mechanistic details have not been discussed.…”