Modeling of the spectroscopy of core electrons with density functional theory

Besley, Nicholas A.

doi:10.1002/wcms.1527

“…From an experimental viewpoint, our ability to generate X-Ray spectra from organic aerosols will be of interest to the theoretical chemistry community. 44 While, theoretical simulations have reached a level of maturity for valence excitations in aqueous systems, 45 there is enormous interest in developing new methods when it comes to core level spectra. 46 Correlations between X-Ray and vibrational spectroscopy at the theoretical level, using the same models of hydrogen bonding networks observed here, will provide a new way to develop an understanding of electronic structure in aqueous organic aerosols.…”

Section: = −mentioning

confidence: 99%

A Direct Probe of the Hydrogen Bond Network in Aqueous Glycerol Aerosols

Weeraratna

¹

,

Amarasinghe

²

,

Lu

³

et al. 2021

J. Phys. Chem. Lett.

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The properties of aerosols are of paramount importance in atmospheric chemistry and human health.The hydrogen bond network of glycerol-water aerosols generated from an aqueous solution with different mixing ratios, is probed directly with X-ray photoelectron spectroscopy. The carbon and oxygen X-ray spectra reveal contributions from gas and condensed phase components of the aerosol.It is shown that water suppresses glycerol evaporation up to a critical mixing ratio. A dielectric analysis using terahertz spectroscopy coupled with Infrared spectroscopy of the bulk solutions provides a picture of the microscopic heterogeneity prevalent in the hydrogen bond network when combined with the photoelectron spectroscopy analysis. The hydrogen bond network is comprised of three intertwined regions. At low concentrations, glycerol molecules are surrounded by water forming a solvated water network. Adding more glycerol leads to a confined water network, maximizing at 22 mol%, beyond which the aerosol resembles bulk glycerol. This microscopic view of hydrogen bonding networks holds promise in probing evaporation, diffusion dynamics and reactivity in aqueous aerosols.

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“…This LR-TDDFT formalism has been adapted for the calculation of core excitation spectra using frozen occupied orbitals, 6,33,[57][58][59] i.e., core/valence separation. We will compare this LR-TDDFT approach to the TKDS approach, for benchmark purposes and to highlight advantages of the latter formalism.…”

Section: Lr-tddftmentioning

confidence: 99%

“…Quantum chemistry is currently witnessing a resurgence of interest in x-ray spectroscopy, [1][2][3][4][5][6][7] catalyzed by the emergence of new technologies including coherent ultrahigh harmonic generation, 8 providing capabilities for ultrafast time resolution at x-ray wavelengths, [9][10][11] even with tabletop laser systems. 12 This technology has enabled x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS) studies of solution-phase systems, [13][14][15][16] as well as surface-sensitive ultrafast spectroscopy at extreme ultraviolet (XUV) wavelengths.…”

Section: Introductionmentioning

confidence: 99%

“…XAS calculations with LR-TDDFT can be rendered tractable by means of an activespace approximation that includes only the core orbitals of interest, along with the full virtual space, such that core-to-valence excitations appear as the lowest states in the spectrum. In many-body theory this approximation is known as "core/valence separation", 1,[30][31][32] whereas in LR-TDDFT it has been called the "restricted excitation window" approach, 6,33 but in either case it amounts to freezing most of the occupied orbitals. For excitations at the K-edge (i.e., those originating from 1s orbitals in the occupied space), this approximation introduces negligible errors of ±0.02 eV, 34 although it is less clear what the errors might be for L-or M-edge excitations.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

Zhu¹,

Alam²,

Herbert

³

2021

Preprint

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We present a protocol for calculation of K-edge x-ray absorption spectra using time-dependent Kohn-Sham (TDKS) calculations, also known as "real-time" time-dependent density functional theory (TDDFT). In principle, the entire absorption spectrum (at all wavelengths) can be computed via Fourier transform of the time-dependent dipole moment function, following a perturbation of the ground-state density and propagation of time-dependent Kohn-Sham molecular orbitals. In practice, very short time steps are required to obtain an accurate spectrum, which increases the cost, but the use of Pade approximants significantly reduces the length of time propagation that is required. Spectra that are well converged with respect to the corresponding linear-response (LR-)TDDFT result can be obtained with < 10 fs of propagation time. Use of complex absorbing potentials helps to remove artifacts at high energies that otherwise result from the use of a finite atom-centered Gaussian basis set. Benchmark results, comparing TDKS to LR-TDDFT, are presented for several small molecules at the carbon and oxygen K-edges, demonstrating good agreement with experiment without the need for specialized basis sets. Whereas LR-TDDFT is a reasonable approach to obtain the near-edge structure, that approach requires hundreds of states and quickly becomes cost prohibitive for large systems, even when the core\slash valence separation approximation is used to remove most of the occupied states from the excitation manifold. We demonstrate the cost-effective TDKS approach by application to a copper dithiolene complex, where binding of a ligand is detectable via shifts in the sulfur K-edge.

show abstract

“…XAS calculations with LR-TDDFT can be rendered tractable by means of an activespace approximation that includes only the core orbitals of interest, along with the full virtual space, such that core-to-valence excitations appear as the lowest states in the spectrum. In many-body theory this approximation is known as "core/valence separation", 1,[30][31][32] whereas in LR-TDDFT it has been called the "restricted excitation window" approach, 6,33 but in either case it amounts to freezing most of the occupied orbitals. For excitations at the K-edge (i.e., those originating from 1s orbitals in the occupied space), this approximation introduces negligible errors of ±0.02 eV, 34 although it is less clear what the errors might be for L-or M-edge excitations.…”

Section: Introductionmentioning

confidence: 99%

Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

Zhu¹,

Alam²,

Herbert

³

2021

Preprint

View full text Add to dashboard Cite

We present a protocol for calculation of K-edge x-ray absorption spectra using time-dependent Kohn-Sham (TDKS) calculations, also known as "real-time" time-dependent density functional theory (TDDFT). In principle, the entire absorption spectrum (at all wavelengths) can be computed via Fourier transform of the time-dependent dipole moment function, following a perturbation of the ground-state density and propagation of time-dependent Kohn-Sham molecular orbitals. In practice, very short time steps are required to obtain an accurate spectrum, which increases the cost, but the use of Pade approximants significantly reduces the length of time propagation that is required. Spectra that are well converged with respect to the corresponding linear-response (LR-)TDDFT result can be obtained with < 10 fs of propagation time. Use of complex absorbing potentials helps to remove artifacts at high energies that otherwise result from the use of a finite atom-centered Gaussian basis set. Benchmark results, comparing TDKS to LR-TDDFT, are presented for several small molecules at the carbon and oxygen K-edges, demonstrating good agreement with experiment without the need for specialized basis sets. Whereas LR-TDDFT is a reasonable approach to obtain the near-edge structure, that approach requires hundreds of states and quickly becomes cost prohibitive for large systems, even when the core\slash valence separation approximation is used to remove most of the occupied states from the excitation manifold. We demonstrate the cost-effective TDKS approach by application to a copper dithiolene complex, where binding of a ligand is detectable via shifts in the sulfur K-edge.

show abstract

Modeling of the spectroscopy of core electrons with density functional theory

Cited by 94 publications

References 233 publications

A Direct Probe of the Hydrogen Bond Network in Aqueous Glycerol Aerosols

A Direct Probe of the Hydrogen Bond Network in Aqueous Glycerol Aerosols

Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

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