Understanding X-ray Photoelectron Spectra of Ionic Liquids: Experiments and Simulations of 1-Butyl-3-methylimidazolium Thiocyanate

Gousseva, Ekaterina; Midgley, Scott D.; Seymour, Jake M.; Seidel, Robert; Grau‐Crespo, Ricardo; Lovelock, Kevin R. J.

doi:10.1021/acs.jpcb.2c06372

Cited by 7 publications

(9 citation statements)

References 112 publications

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“…Our first example is an ion-pair dimer, 1-butyl-3-methylimidazolium (C 4 C 1 Im + ) with a thiocyanate (SCN – ) counter-ion, representing a typical dialkylimidazolium ionic liquid . This and other room-temperature ionic liquids have been studied using NEXAFS spectroscopy at the nitrogen and sulfur K-edges .…”

Section: Resultsmentioning

confidence: 99%

“…Our first example is an ion-pair dimer, 1-butyl-3-methylimidazolium (C 4 C 1 Im + ) with a thiocyanate (SCN − ) counter-ion, representing a typical dialkylimidazolium ionic liquid. 124 This and other room-temperature ionic liquids have been studied using NEXAFS spectroscopy at the nitrogen and sulfur K-edges. 125 In accompanying calculations, it was observed that excited states could be delocalized across the ion pair in some cases, 125 such that computational modeling should not be limited to either the cation or the anion.…”

Section: A Comparison Of Tdks To Lr-tddftmentioning

confidence: 99%

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Time-Dependent Density Functional Theory for X-ray Absorption Spectra: Comparing the Real-Time Approach to Linear Response

Herbert,

Zhu,

Alam

et al. 2023

J. Chem. Theory Comput.

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We simulate X-ray absorption spectra at elemental K-edges using time-dependent density functional theory (TDDFT) in both its conventional linear-response implementation and its explicitly time-dependent or “real-time” formulation. Real-time TDDFT simulations enable broadband spectra calculations without the need to invoke frozen occupied orbitals (“core/valence separation”), but we find that these spectra are often contaminated by transitions to the continuum that originate from lower-energy core and semicore orbitals. This problem becomes acute in triple-ζ basis sets, although it is sometimes sidestepped in double-ζ basis sets. Transitions to the continuum acquire surprisingly large dipole oscillator strengths, leading to spectra that are difficult to interpret. Meaningful spectra can be recovered by means of a filtering technique that decomposes the spectrum into contributions from individual occupied orbitals, and the same procedure can be used to separate L- and K-edge spectra arising from different elements within a given molecule. In contrast, conventional linear-response TDDFT requires core/valence separation but is free of these artifacts. It is also significantly more efficient than the real-time approach, even when hundreds of individual states are needed to reproduce near-edge absorption features and even when Padé approximants are used to reduce the real-time simulations to just 2–4 fs of time propagation. Despite the cost, the real-time approach may be useful to examine the validity of the core/valence separation approximation.

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Section: Resultsmentioning

confidence: 99%

Section: A Comparison Of Tdks To Lr-tddftmentioning

confidence: 99%

Time-Dependent Density Functional Theory for X-ray Absorption Spectra: Comparing the Real-Time Approach to Linear Response

Herbert,

Zhu,

Alam

et al. 2023

J. Chem. Theory Comput.

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“…can also be used as a secondary measure of the anion-dependent interaction strength ( Figure 2 b), although E B (N cation 1s,exp.) is usually used, as C anion 1s peaks can overlap with C hetero 1s and C 2 1s peaks, e.g., for [SCN] − -based ILs, 66 making fitting more challenging when obtaining E B (C hetero 1s,exp.) and E B (C 2 1s,exp.)…”

Section: Methodsmentioning

confidence: 99%

“…This conclusion was based on the fact that initial-state calculations gave excellent visual matches for the N 1s and final-state calculations for S 2p and N 1s in the anion [SCN] − gave the same trends as initial-state calculations. 66 However, no results were presented on anion-dependent interactions. Hence, whether the XPS-derived anion-dependent interaction strength scale is due to initial-state effects or final-state effects is still an open question.…”

Section: Introductionmentioning

confidence: 99%

Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Gousseva,

Towers Tompkins,

Seymour

et al. 2024

J. Phys. Chem. B

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Using a combination of experiments and calculations, we have gained new insights into the nature of anion−cation interactions in ionic liquids (ILs). An X-ray photoelectron spectroscopy (XPS)-derived anion-dependent electrostatic interaction strength scale, determined using XPS core-level binding energies for IL cations, is presented here for 39 different anions, with at least 18 new anions included. Linear correlations of experimental XPS core-level binding energies for IL cations with (a) calculated core binding energies (ab initio molecular dynamics (AIMD) simulations were used to generate high-quality model IL structures followed by single-point density functional theory (DFT) to obtain calculated core binding energies), (b) experimental XPS core-level binding energies for IL anions, and (c) other anion-dependent interaction strength scales led to three main conclusions. First, the effect of different anions on the cation can be related to ground-state interactions. Second, the variations of anion-dependent interactions with the identity of the anion are best rationalized in terms of electrostatic interactions and not occupied valence state/unoccupied valence state interactions or polarizability-driven interactions. Therefore, the XPS-derived anion-dependent interaction strength scale can be explained using a simple electrostatic model based on electrostatic site potentials. Third, anion−probe interactions, irrespective of the identity of the probe, are primarily electrostatic, meaning that our electrostatic interaction strength scale captures some inherent, intrinsic property of anions independent of the probe used to measure the interaction strength scale.

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“…Our first example is an ion-pair dimer, 1-butyl-3-methylimidazolium (C 4 C 1 Im + ) and thiocyanate (SCN − ), representing a typical dialkylimidazolium ionic liquid. 94 This and other roomtemperature ionic liquids have been using NEXAFS spectroscopy at the nitrogen and sulfur K-edges. 95 In ac- The complete TDKS spectrum ("full") is compared to filtered spectra involving only the O(1s), N(1s), or S(2p) orbitals, as indicated.…”

Section: B Continuum Artifacts Figurementioning

confidence: 99%

Time-dependent density functional theory for x-ray absorption spectra: Comparing the real-time approach to linear response

Herbert

Zhu

Alam

et al. 2023

Preprint

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We examine the simulation of x-ray absorption spectra at elemental K-edges using time-dependent density functional theory, in both its conventional linear-response implementation and also its "real-time" formulation. Real-time simulations enable broadband x-ray spectra calculations without the need to invoke frozen occupied orbitals or "core/valence separation", but we find that the spectra are frequently contaminated by transitions to the continuum originating from lower-energy core and semi-core orbitals. This problem becomes acute in triple-zeta basis sets although it is sometimes bypassed serendipitously in lower-quality basis sets. Transitions to the continuum acquire surprisingly large dipole oscillator strengths, leading to spectra that are difficult or impossible to interpret. Meaningful spectra can be recovered by means of a filtering technique that decomposes the spectrum into contributions from individual occupied orbitals, and the same procedure can be used to separate L- and K-edge spectra. Nevertheless, the conventional linear-response approach is significantly more efficient even when hundreds of individual states are needed to reproduce near-edge absorption features, and even when Pade approximants are used to reduce the real-time simulations to less than 2 fs of time propagation. The real-time approach may be useful for examining the validity of core/valence separation, however.

show abstract

Understanding X-ray Photoelectron Spectra of Ionic Liquids: Experiments and Simulations of 1-Butyl-3-methylimidazolium Thiocyanate

Cited by 7 publications

References 112 publications

Time-Dependent Density Functional Theory for X-ray Absorption Spectra: Comparing the Real-Time Approach to Linear Response

Time-Dependent Density Functional Theory for X-ray Absorption Spectra: Comparing the Real-Time Approach to Linear Response

Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory

Time-dependent density functional theory for x-ray absorption spectra: Comparing the real-time approach to linear response

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