Time Dependent Density Functional Theory of X-ray Absorption Spectroscopy of Alkaline-Earth Oxides

Fronzoni, G.; Francesco, R. De; Stener, Mauro

doi:10.1021/jp050755y

Cited by 31 publications

(34 citation statements)

References 39 publications

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“…However, it has been shown that these operators have little effect on relative transition energies 77 and uniform shifts are routinely applied to calculated XANES spectra to better compare transition energies with experimental data. 77–79 A uniform shift of 172 eV is applied to all calculated spectra and all transitions are convoluted with Gaussian functions to match experimental lineshapes; 2.2 and 1.8 eV FWHM for the 4p z and 3d transitions respectively.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

et al. 2016

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Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state,1,2 structural dynamics before thermalization were not resolved due to the ~100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray Absorption Near Edge Structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex’s geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a timescale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.

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Section: Resultsmentioning

confidence: 99%

Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

et al. 2016

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“…We apply a uniform shift to the calculated spectrum such that the lowest energy peak perfectly matches the experimental value, as is done in other studies. 18,56,57 The errors are then calculated using the remaining transitions. Table 1 shows the error analysis of predicted K-edge spectra with the ES-TDDFT method.…”

Section: Resultsmentioning

confidence: 99%

Calibration of Energy-Specific TDDFT for Modeling K-edge XAS Spectra of Light Elements

Lestrange

Nguyen

2015

J. Chem. Theory Comput.

116

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X-ray absorption spectroscopy (XAS) has become a powerful technique in chemical physics, because of advances in synchrotron technology that have greatly improved its temporal and spectroscopic resolution. Our recent work on energy-specific time-dependent density functional theory (ES-TDDFT) allows for the direct calculation of excitation energies in any region of the absorption spectrum, from UV-vis to X-ray. However, the ability of different density functional theories to model X-ray absorption spectra (XAS) of light elements has not yet been verified for ES-TDDFT. This work is a calibration of the ability of existing DFT kernels and basis sets to reproduce experimental K-edge excitation energies. Results were compared against 30 different transitions from gas-phase experiments. We focus on six commonly used density functionals (BHandHLYP, B3LYP, PBE1PBE, BP86, HSE06, LC-ωPBE) and various triple-ζ basis sets. The effects of core and diffuse functions are also investigated.

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“…However, it has been shown that these operators have little effect on relative transition energies 60 and uniform shifts are routinely applied to calculated XANES spectra to better compare transition energies with experimental data. 60–62 A uniform shift of 172 eV (~2% of the Ni K-edge energy) is applied to all calculated spectra and all transitions are convoluted with Gaussian functions to match experimental lineshapes; 2.2 and 1.8 eV FWHM for the 4p z and 3d transitions respectively.…”

Section: Resultsmentioning

confidence: 99%

Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

et al. 2016

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This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3dx2−y2) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.

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Time Dependent Density Functional Theory of X-ray Absorption Spectroscopy of Alkaline-Earth Oxides

Cited by 31 publications

References 39 publications

Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

Calibration of Energy-Specific TDDFT for Modeling K-edge XAS Spectra of Light Elements

Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

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