Perturbation Theory Calculations Research Articles

Anion Photoelectron Spectroscopy and Ab Initio Studies of the UF- Anion.

A synergistic anion photoelectron spectroscopic and ab initio computational study of photodetachment of UF- is reported. The measurement determined a vertical detachment energy of 0.63(03) eV, which is consistent with a spinor-based relativistic coupled-cluster CCSD(T) value of 0.61 eV. The complex spectral features due to excited electronic states and vibrational progressions of UF are analyzed and assigned with the help of spin-orbit-coupled multireference perturbation theory and spinor-based relativistic coupled-cluster calculations. UF and UF- are confirmed to be dominated by ionic bonding. The usefulness of the spinor CCSD(T) approach is demonstrated.

Achieving Sub-ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework.

We report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine-functionalized COF (SonoCOF-9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g-1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g-1 with excellent reversibility for at least 50 adsorption-desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled -42.3 kJ mol-1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller-Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF-9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub-ppm level (0.0064 ppm of SO2).

Achieving Sub‐ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework

AbstractWe report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine‐functionalized COF (SonoCOF‐9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g−1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g−1 with excellent reversibility for at least 50 adsorption‐desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled −42.3 kJ mol−1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller–Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF‐9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub‐ppm level (0.0064 ppm of SO2).

Cyclic and helical symmetry-informed machine learned force fields: Application to lattice vibrations in carbon nanotubes

We present a formalism for developing cyclic and helical symmetry-informed machine learned force fields (MLFFs). In particular, employing the smooth overlap of atomic positions descriptors with the polynomial kernel method, we derive cyclic and helical symmetry-adapted expressions for the energy, atomic forces, and phonons, i.e., lattice vibration frequencies and modes. We use this formulation to construct a symmetry-informed MLFF for carbon nanotubes (CNTs), where the model is trained through Bayesian linear regression, with the data generated from ab initio density functional theory (DFT) calculations performed during on-the-fly symmetry-informed MLFF molecular dynamics simulations of representative CNTs. We demonstrate the accuracy of the MLFF model by comparisons with DFT calculations for the energies and forces, and density functional perturbation theory calculations for the phonons, while considering CNTs not used in the training. In particular, we obtain a root mean square error of 1.4×10−4 Ha/atom, 4.7×10−4 Ha/Bohr, and 4.8 cm−1 in the energy, forces, and phonon frequencies, respectively, which are well within the accuracy targeted in ab initio calculations. We apply this framework to study phonons in CNTs of various diameters and chiralities, where we identify the torsional rigid body mode that is unique to cylindrical structures and establish laws for variation of the phonon frequencies associated with the ring modes and radial breathing modes. Overall, the proposed formalism provides an avenue for studying nanostructures with cyclic and helical symmetry at ab initio accuracy, while providing orders-of-magnitude speedup relative to such methods.

Ca3[C2O5]2[CO3] is a pyrocarbonate which can be formed at p, T-conditions prevalent in the Earth’s transition zone

Understanding the fate of subducted carbonates is a prerequisite for the elucidation of the Earth’s deep carbon cycle. Here we show that the concomitant presence of Ca[CO3] with CO2 in a subducting slab very likely results in the formation of an anhydrous mixed pyrocarbonate, Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document}, at moderate pressure ( ≈ 20 GPa) and temperature ( ≈ 1500 K) conditions. We show that at these conditions Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} can be obtained by reacting Ca[CO3] with CO2 in a laser-heated diamond anvil cell. The crystal structure was obtained from synchrotron-based single crystal X-ray diffraction data. Density Functional Perturbation Theory calculations in combination with experimental Raman spectroscopy results unambiguously confirmed the structural model. The crystal structure of Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} is characterized by the presence of CO32−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\left[{{{{\\rm{CO}}}}}_{3}\\right]}^{2-}$$\\end{document}- and C2O52−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}^{2-}$$\\end{document}-groups. The results presented here imply that the formation of Ca3C2O52CO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{\\rm{Ca}}}}}_{3}{\\left[{{{{\\rm{C}}}}}_{2}{{{{\\rm{O}}}}}_{5}\\right]}_{2}\\left[{{{{\\rm{CO}}}}}_{3}\\right]$$\\end{document} needs to be taken into account when constructing models of the deep carbon cycle of the Earth.

Exploring the potential of α-Ge(1 1 1) monolayer in photocatalytic water splitting for hydrogen production

In this study, the structural, electronic, and optical properties of 2D α-Ge(1 1 1) are investigated using Density Functional Theory (DFT) calculations, complemented by many-body perturbation theory calculations based on the GW/BSE approach. The thermodynamic stability of this material is assessed through ab initio molecular dynamics simulations (AIMD), and their dynamic stability is confirmed via phonon dispersion calculations. The analysis of the optical properties reveals significant absorption peaks in both visible and ultraviolet regions, with an absorption edge at 47 eV (1.87 eV without excitonic effects). The band edges are well-aligned with water redox potentials at neutral pH, making them suitable for water-splitting applications. For other pH levels, we find the process may be feasible through the participation of different excited states populated by light absorption. Remarkably, the α-Ge(1 1 1) monolayer demonstrates a predicted solar-to-hydrogen conversion efficiency of 34.80 %, outperforming many other two-dimensional materials. These findings position the α-Ge(1 1 1) monolayer as a promising candidate for developing efficient photocatalytic materials for hydrogen generation via overall water splitting.

Exploring Ion Polarizabilities and Their Correlation with van der Waals Radii: A Theoretical Investigation.

Polarizability (α) is a fundamental property which measures the tendency of the electron cloud of an atom, ion, or molecule to be distorted by electric field. Polarizability contributes to important physical properties such as molecular interactions or dielectric constants; thus, it is essential to have accurate polarizabilities in molecular simulations. However, it remains a challenge to develop polarizable force fields (FFs) for ions in computational chemistry. In particular, a comprehensive set of polarizabilities for ions has not been derived. Herein, we derived a systematic set of polarizabilities for atoms and ions across the periodic table based on high-level quantum mechanics calculations. These values have excellent agreement with experimental data. Furthermore, we examined the relationship between the obtained polarizabilities and the van der Waals (VDW) radii (RVDW) that we previously determined (J. Chem. Theory Comput., 2023, 19, 2064). Two relationships, RVDW ∝ α1/7 and RVDW ∝ α1/3, proposed in previous studies were examined in the present work. Our results indicated the former relationship, which was derived based on the quantum harmonic oscillator model, prevails for atoms and cations, but neither relationship provides a satisfactory fit for anions. This is consistent with the tight-binding nature of the electrons in atoms and cations, while it is more challenging to quantify the polarizabilities of anions because of their more dispersed electron clouds. Moreover, we compared different approaches to determine the dispersion coefficients, including the London equation, Slater-Kirkwood equation, symmetry-adapted perturbation theory (SAPT) calculations, and time-dependent density functional theory method, along with the approach based on VDW constants. Our results indicated that although different approaches predict deviated magnitudes for the dispersion coefficients, their predictions are highly correlated, implying that each of these approaches can be used to evaluate dispersion interactions after proper scaling. Finally, we have developed a parametrization strategy for the 12-6-4 model based on the obtained insights. We specifically compared the performance of the 12-6-4 model with SAPT and SobEDA analyses to model interactions involving Na+/Mg2+ and various ligands containing He, Ne, Ar, H2O, NH3, [H2PO4]-, and [HPO4]2-. Our results demonstrate that the 12-6-4 parameters effectively reproduce both the total interaction energy and the individual energy components (electrostatics, exchange-repulsion, dispersion, and induction), highlighting the physical robustness of the 12-6-4 model and the effectiveness of our parametrization approach. This study has significant implications for advancing the development of next-generation ion models and polarizable FFs.

Two-Gap Superconductivity and the Decisive Role of Rare-Earth d Electrons in Infinite-Layer Nickelates.

We present a theoretical prediction of a phonon-mediated two-gap superconductivity in infinite-layer nickelates Nd_{1-x}Sr_{x}NiO_{2} by performing abinitio GW and GW perturbation theory calculations. Electron GW self-energy effects significantly alter the characters of the two-band Fermi surface and enhance the electron-phonon coupling, compared with results based on density functional theory. Solutions of the fully k-dependent anisotropic Eliashberg equations yield two dominant s-wave superconducting gaps-a large gap on a band of rare-earth Nd d and interstitial orbital characters and a small gap on a band of transition-metal Ni d character. Increasing hole doping induces a non-rigid-band response in the electronic structure, leading to a rapid drop of the superconducting T_{c} in the overdoped regime in agreement with experiments.

Predicting exciton binding energies from ground-state properties

We systematically investigate the correlations between exciton binding energies and various easily calculated ground-state properties (“predictors”) that have been proposed to correlate with them. We do so for 51 bulk compounds, ranging from simple binary semiconductors to more exotic materials such as noble gas solids, perovskites, and layered systems and show that using only a few easily calculable parameters, a broadly applicable clustering of materials according to their exciton binding energies is possible. While no single one of the proposed parameters satisfactorily predicts the exciton binding energy, a combination of several parameters that enter the Wannier-Mott model or characterize the nature of the valence band and the ionicity of the compound allows a reliable automated clustering of exciton binding energies. The results allow an efficient estimation of the importance of excitonic effects without the need for expensive many-body perturbation theory calculations or other advanced numerically demanding approaches. Published by the American Physical Society 2024

Web-CONEXS: an inroad to theoretical X-ray absorption spectroscopy.

Accurate analysis of the rich information contained within X-ray spectra usually calls for detailed electronic structure theory simulations. However, density functional theory (DFT), time-dependent DFT and many-body perturbation theory calculations increasingly require the use of advanced codes running on high-performance computing (HPC) facilities. Consequently, many researchers who would like to augment their experimental work with such simulations are hampered by the compounding of nontrivial knowledge requirements, specialist training and significant time investment. To this end, we present Web-CONEXS, an intuitive graphical web application for democratizing electronic structure theory simulations. Web-CONEXS generates and submits simulation workflows for theoretical X-ray absorption and X-ray emission spectroscopy to a remote computing cluster. In the present form, Web-CONEXS interfaces with three software packages: ORCA, FDMNES and Quantum ESPRESSO, and an extensive materials database courtesy of the Materials Project API. These software packages have been selected to model diverse materials and properties. Web-CONEXS has been conceived with the novice user in mind; job submission is limited to a subset of simulation parameters. This ensures that much of the simulation complexity is lifted and preliminary theoretical results are generated faster. Web-CONEXS can be leveraged to support beam time proposals and serve as a platform for preliminary analysis of experimental data.

Toward extracting the scattering phase shift from integrated correlation functions. II. A relativistic lattice field theory model

In the present work, a relativistic relation that connects the difference of interacting and noninteracting integrated two-particle correlation functions in finite volume to infinite volume scattering phase shift through an integral is derived. We show that the difference of integrated finite volume correlation functions converges rapidly to its infinite volume limit as the size of the periodic box is increased. The fast convergence of our proposed formalism is illustrated by analytic solutions of a contact interaction model, the perturbation theory calculation, and also the Monte Carlo simulation of a complex ϕ4 lattice field theory model. Published by the American Physical Society 2024

Non-adiabatic electronic relaxation of tetracene from its brightest singlet excited state.

The ultrafast relaxation dynamics of tetracene following UV excitation to the bright singlet state S6 has been studied with time-resolved photoelectron spectroscopy. With the help of high-level abinitio multireference perturbation theory calculations, we assign photoelectron signals to intermediate dark electronic states S3, S4, and S5 as well as to a low-lying electronic state S2. The energetic structure of these dark states has not been determined experimentally previously. The time-dependent photoelectron yields assigned to the states S6, S5, and S4 have been analyzed and reveal the depopulation of S6 within 60fs, while S5 and S4 are populated with delays of about 50 and 80fs. The dynamics of the lower-lying states S3 and S2 seem to agree with a delayed population coinciding with the depopulation of the higher-lying states S4-S6 but could not be elucidated in full detail due to the low signal levels of the corresponding two-photon ionization probe processes.

Taxifolin Adsorption on Nitrogenated Graphenes: Theoretical Insights

Solid-state drug delivery systems for the drug substances transport are of great importance nowadays. In the present work, the non-covalent interactions between taxifolin (Tax) and graphene as well as nitrogenated (N-doped) graphenes were systematically studied by using a wide set of theoretical techniques. Symmetry-adapted perturbation theory (SAPT0) calculations confirmed more favorable adsorption of Tax on N-doped graphenes compared to pristine graphene. It was established that dispersion interactions play the main role in the attractive interactions (>60%), whereas electrostatic and induction forces contribute only moderately to the attraction (~25% and 7–8%, respectively). Independent gradient model (IGM) analysis visually demonstrated the existence of dispersion interactions and hydrogen bonding in the studied Tax complexes. Ab initio molecular dynamics calculations indicated stability of these complexes at different temperatures. Our results show that N-doped graphenes with the enhanced interaction energy (Eint) toward Tax are promising candidates for the technical realization of the targeted drug delivery systems.

Gravitational waves and tadpole resummation: Efficient and easy convergence of finite temperature QFT

We demonstrate analytically and numerically that “optimized partial dressing” (OPD) thermal mass resummation, which uses gap equation solutions inserted into the tadpole, efficiently tames finite-temperature perturbation theory calculations of the effective thermal potential, without necessitating use of the high-temperature approximation. An analytical estimate of the scale dependence for OPD resummation, standard Parwani resummation (Daisy resummation), and dimensional reduction shows that OPD has similar scale dependence to dimensional reduction, greatly improving Parwani resummation. We also elucidate how to construct and solve the gap equation for realistic numerical calculations, and demonstrate OPD’s improved accuracy for a toy scalar model. OPD’s improved accuracy is most physically significant when the high-temperature approximation breaks down, rendering dimensional reduction unusable and Parwani resummation highly inaccurate, with the latter underestimating the maximal gravitational wave amplitude for the model by 2 orders of magnitude compared to OPD. Our work highlights the need to bring theoretical uncertainties under control even when analyzing broad features of a model. Given the simplicity of the OPD compared to two-loop dimensional reduction, as well as the ease with which this scheme handles departures from the high-temperature expansion, we argue this scheme has great potential in analyzing the parameter space of realistic beyond the Standard Model models. Published by the American Physical Society 2024

Can Pressure be a Good Strategy for Optimizing Thermoelectric Performance of SnPS3${\rm SnPS}_3$?

AbstractExternal pressure can significantly alter the transport coefficients, power factor, and figure of merit because of its direct influence on the electronic structure, electron–phonon, and phonon–phonon couplings. This study delves into the electronic and thermal transport properties of at external pressures up to 30 GPa using first‐principles calculations and Boltzmann transport theory. The electron–phonon relaxation time is computed within the electron–phonon‐averaged (EPA) approximation, enabling exploration beyond the constant relaxation time approximation. The first‐principles calculations reveal an indirect bandgap of 1.76 (without pressure) and 0.12 eV (30 GPa). The density functional perturbation theory calculations confirm the dynamic stability of at external pressure up to 30 GPa. The electronic transport properties are improved by more than one order of magnitude at 30 GPa, consistent with experimental observations. The Peierls–Boltzmann transport calculations demonstrate the room temperature lattice thermal conductivity of 0.22 (without pressure) and 7.4 (at 30 GPa). The results emanate that exhibits of 0.71 at 900 K at a hole doping of 2 at zero pressure, which decreases with increasing pressure. The findings explore the effect of external pressure on both electronic and thermal transport properties of , warranting further experimental exploration of thermal transport properties at higher pressures.

Analytically separating the source of the Teukolsky equation

Recent gravitational wave detections from black hole mergers have underscored the critical role black hole perturbation theory and the Teukolsky equation play in understanding the behavior of black holes. The separable nature of the Teukolsky equation has long been leveraged to study the vacuum linear Teukolsky equation; however, as theory and measurements advance, solving the sourced Teukolsky equation is becoming a frontier of research. In particular, second-order calculations, such as in quasinormal mode and self-force problems, have extended sources. This paper presents a novel method for analytically separating the Teukolsky equation’s source, aimed to improve efficiency. Separating the source is a nontrivial problem due to the angular and radial mixing of generic quantities in Kerr spacetime. We provide a proof-of-concept demonstration of our method and show that it is accurate, separating the Teukolsky source produced by the stress-energy tensor of an ideal gas cloud surrounding a Kerr black hole. The detailed application of our method is provided in an accompanying notebook. Our approach opens up a new avenue for accurate black hole perturbation theory calculations with sources in both the time and frequency domain. Published by the American Physical Society 2024

ExROPPP: Fast, accurate, and spin-pure calculation of the electronically excited states of organic hydrocarbon radicals.

Recent years have seen an explosion of interest in organic radicals due to their promise for highly efficient organic light-emitting diodes and molecular qubits. However, accurately and inexpensively computing their electronic structure has been challenging, especially for excited states, due to the spin-contamination problem. Furthermore, while alternacy or "pseudoparity" rules have guided the interpretation and prediction of the excited states of closed-shell hydrocarbons since the 1950s, similar general rules for hydrocarbon radicals have not to our knowledge been found yet. In this article, we present solutions to both of these challenges. First, we combine the extended configuration interaction singles method with Pariser-Parr-Pople (PPP) theory to obtain a method that we call ExROPPP (Extended Restricted Open-shell PPP) theory. We find that ExROPPP computes spin-pure excited states of hydrocarbon radicals with comparable accuracy to experiment as high-level general multi-configurational quasi-degenerate perturbation theory calculations but at a computational cost that is at least two orders of magnitude lower. We then use ExROPPP to derive widely applicable rules for the spectra of alternant hydrocarbon radicals, which are completely consistent with our computed results. These findings pave the way for highly accurate and efficient computation and prediction of the excited states of organic radicals.

DFT Struggles to Predict the Energy Landscape for Iron Pyridine Diimine-Catalyzed [2 + 2] Cycloaddition of Alkenes: Insights into the Problem and Alternative Solutions.

In recent years, noninnocent pyridine diimine (PDI) complexes featuring first-row transition metals have emerged as prominent catalysts, demonstrating efficacy in a diverse range of vital organometallic transformations. However, the inherent complexity of the fundamental reactivity paradigm in these systems arises from the presence of a noninnocent ligand and the multispin feasibility of 3d metals. While density functional theory (DFT) has been widely used to unravel mechanistic insights, its limitations as a single-reference method can potentially misrepresent spin-state energetics, compromising our understanding of these intricate systems. In this study, we employ extensive high-level ab initio state averaged-complete active space self-consistent field/N-electron valence state perturbation theory (SA-CASSCF/NEVPT2) calculations in combination with DFT to investigate an iron-PDI-catalyzed [2 + 2] cycloaddition reaction of alkenes. The transformation proceeds through two major steps: oxidative cyclization and reductive elimination. Contrary to the predictions of DFT calculations, which suggest two-state reactivity in the reaction and identify reductive elimination as the turnover-limiting step, SA-CASSCF/NEVPT2-corrected results unequivocally establish a single-state reactivity scenario with oxidative cyclization as the turnover-limiting step. SA-CASSCF/NEVPT2-based insights into electronic ground states and electron distribution elucidate the intriguing interactions between the PDI ligand and the iron center, revealing the highly multiconfigurational nature of these species and providing a precise depiction of metal-ligand cooperativity throughout the transformation. A comparative assessment of several widely recognized DFT functionals against SA-CASSCF/NEVPT2-corrected data indicates that single-point energy calculations using the modern density functional MN15 on TPSSh geometries offer the most reliable density functional methodology, in scenarios where SA-CASSCF/NEVPT2 computational cost is a consideration.

Probing Ion-Receptor Interactions in Halide Complexes of Octamethyl Calix[4]Pyrrole.

Ion receptors are molecular hosts that bind ionic guests, often with great selectivity. The interplay of solvation and ion binding in anion host-guest complexes in solution governs the binding efficiency and selectivity of such ion receptors. To gain molecular-level insight into the intrinsic binding properties of octamethyl calix[4]pyrrole (omC4P) host molecules with halide guest ions, we performed cryogenic ion vibrational spectroscopy (CIVS) of omC4P in complexes with fluoride, chloride, and bromide ions. We interpret the spectra using density functional theory, describing the infrared spectra of these complexes with both harmonic and anharmonic second-order vibrational perturbation theory (VPT2) calculations. The NH stretching modes of the pyrrole moieties serve as sensitive probes of the ion binding properties, as their frequencies encode the ion-receptor interactions. While scaled harmonic spectra reproduce the experimental NH stretching modes of the chloride and bromide complexes in broad strokes, the high proton affinity of fluoride introduces strong anharmonic effects. As a result, the spectrum of F-·omC4P is not even qualitatively captured by harmonic calculations, but it is recovered very well by VPT2 calculations. In addition, the VPT2 calculations recover the intricate coupling of the NH stretching modes with overtones and combination bands of CH stretching and NH bending modes and with low-frequency vibrations of the omC4P macrocycle, which are apparent for all of the halide ion complexes investigated here. A comparison of the CIVS spectra with infrared spectra of solutions of the same ion-receptor complexes in d3-acetonitrile and d6-acetone shows how ion solvation changes the ion-receptor interactions for the different halide ions.

Comments on “Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding”

AbstractIn a recent communication (Angew. Chem. Int. Ed. 2024, 63, e202317312), Kalita et al. studied In4H+ system within the frame of single‐reference approximation (SRA) and found that the global energy minimum (1 a) adopted the singlet state and a planar tetracoordinate hydrogen (ptH), while the second lowest isomer (1 b) located 3.0 kcal/mol above 1 a and adopted the triplet state as well as non‐planar structure with a quasi‐ptH. They assessed the reliability of SRA by checking the T1‐diagnostic values of coupled cluster calculations. However, according to our multi‐configurational second‐order perturbation theory calculations at the CASPT2(12,13)/aug‐cc‐pVQZ (aug‐cc‐pVQZ‐PP for In) level, both 1 a and 1 b exhibit obvious multi‐referential characters, as reflected by their largest reference coefficients of 0.928 (86.1 %) and 0.938 (88.0 %), respectively. Moreover, 1 b is 5.05 kcal/mol lower than 1 a at this level, that is, what can be observed in In4H+ system is the quasi‐ptH.