Electronic Energy Difference Research Articles

Chiral kagome superconductivity modulations with residual Fermi arcs.

Superconductivity involving finite-momentum pairing1 can lead to spatial-gap and pair-density modulations, as well as Bogoliubov Fermi states within the superconducting gap. However, the experimental realization of their intertwined relations has been challenging. Here we detect chiral kagome superconductivity modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5 using normal and Josephson scanning tunnelling microscopy down to 30 millikelvin with a resolved electronic energy difference at the microelectronvolt level. We observe a U-shaped superconducting gap with flat residual in-gap states. This gap shows chiral 2a×2a spatial modulations with magnetic-field-tunable chirality, which align with the chiral 2a×2a pair-density modulations observed through Josephson tunnelling. These findings demonstrate a chiral pair density wave (PDW) that breaks time-reversal symmetry. Quasiparticle interference imaging of the in-gap zero-energy states reveals segmented arcs, with high-temperature data linking them to parts of the reconstructed vanadium d-orbital states within the charge order. The detected residual Fermi arcs can be explained by the partial suppression of these d-orbital states through an interorbital 2a×2a PDW and thus serve as candidate Bogoliubov Fermi states. In addition, we differentiate the observed PDW order from impurity-induced gap modulations. Our observations not only uncover a chiral PDW order with orbital selectivity but also show the fundamental space-momentum correspondence inherent in finite-momentum-paired superconductivity.

Quantum mechanical treatment for potential antiphlogistic effects from the leaf extract of Ocimum basilicum citriodorum using gas chromatography-mass spectrometry (GCMS)

Abstract The immune biological response systems and inflammation can be triggered by a number of things such as pathogens, damaged cells and toxic substances. In ethnomedicine, leaves of Lemon basil (Ocimum basilicum citriodorum) have been used for their health benefits. This study examines the anti-inflammatory properties of lemon basil stalks. In a GC/MS study, 24 plant-based bioactive compounds were identified. Comparing the activities in 24 compounds with the largest negative binding energy values helped us determine which compound was most active. It can be seen that only two compounds (Campstool and stigmasterol) with the highest binding energies interact with the 2QVD protein; consequently, the compound with the highest binding energy has superior anti-inflammatory activity. In quantum mechanics, electron energy difference between lowest-unoccupied molecular orbitals (LUMO) and highest-occupied molecular orbitals (HOMO) is described by the quantum-mechanical method, electronegativity (χ), electron affinity (A), global hardness (η), global softness (σ) and ionization potential (I) estimated from the optimized structure. Higher energy molecules are more reactive than other substances reported in this study.

Predicting spin states of iron porphyrins with DFT methods including crystal packing effects and thermodynamic corrections.

Accurate computational treatment of spin states for transition metal complexes, exemplified by iron porphyrins, lies at the heart of quantum bioinorganic chemistry, but at the same time represents a great challenge for approximate density functional theory (DFT) methods, which are predominantly used. Here, the accuracy of DFT methods for spin-state splittings in iron porphyrin is assessed by probing the ability to correctly predict the ground states for six FeIII or FeII complexes experimentally characterized in solid state. For each case, molecular and periodic DFT calculations are employed to quantify the effect of porphyrin side substituents and the crystal packing effect (CPE) on the spin-state splitting. It is proposed to partition the total CPE into additive components, the direct and structural one, the importance of which is shown to significantly vary from case to case. By knowing the substituent effect, the CPE, and the Gibbs free energy thermodynamic correction from calculations, one can employ the experimental ground-state information in order to derive a quantitative constraint on the electronic energy difference for a simplified (porphin) model of the experimentally characterized metalloporphyrin. The constraints derived in such a way-in the form of single or double inequalities-are used to assess the accuracy of dispersion-corrected DFT methods for 6 spin-state splittings of [FeIII(P)(2-MeIm)2]+, [FeIII(P)(2-MeIm)]+, [FeII(P)(THF)2] and [FeII(P)] models (where P is porphin, 2-MeIm is 2-methylimidazole, THF is tetrahydrofuran). These data constitute the new benchmark set of spin states for crystalline iron porphyrins (SSCIP6). The highest accuracy is obtained in the case of double-hybrid functionals (B2PLYP-D3, DSD-PBEB95-D3), whereas hybrid functionals, especially those with reduced admixture of the exact exchange (B3LYP*-D3, TPSSh-D3), are found to considerably overstabilize the intermediate spin state, leading to incorrect ground-state prediction in FeIII porphyrins. The present approach, which can be generalized to other transition metal complexes, is not only useful in method benchmarking, but also sheds light on the interpretations of experimental data for metalloporphyrins, which are important models to understand the electronic properties of heme proteins.

An Algorithm Predicting the Optimal Mechanical Response of Electronic Energy Difference.

The use of mechanical forces at the molecular level has been shown to be an interesting tool for modulating different chemical and physical molecular properties. The so-called covalent mechanochemistry deals with the application of precise mechanical forces that induce specific changes in the structure, stability, reactivity, and other physical properties. The use of this kind of force to modulate photophysical properties and photochemical reactivity has also been studied. Nevertheless, the general problem of mechanical modulation of the energy gap between two electronic states has been addressed only with the development of simple theoretical models. Here, we develop and implement an algorithm providing the Largest energy Gap variation with Minimal mechanical Force (LGMF) that allows the determination of the optimal mechanical forces tuning the electronic energy gap, as well as to identify the maximum mechanical response of a molecular system to the application of any mechanical stimulus. The algorithm has been implemented for diverse molecular systems showing different degrees of flexibility. The phyton code of the algorithm is available in a public repository.

Small palladium clusters and their adducts with atomic oxygen

A systematic investigation on small Pdn clusters (n = 1 ÷ 8) and their interaction with atomic oxygen was conducted at DFT level. A model to describe cohesive energy for small sized clusters based on a topological approach was proposed and validated. On the basis of the bond length, the stabilisation electronic energy and the second electronic energy difference variation analysis, Pd4 and Pd6 were identified as the most stable clusters. The Natural Bond Orbital (NBO) analysis and the plot of the Molecular Electrostatic Potential (MEP) – both performed for the first time – indicated that the Pd atoms in clusters were not equivalent in terms of atomic charge, population and electron configuration. The plots of the MEP mapped on the electron density also revealed its non-uniform character; areas of positive MEP were found around the Pd atoms, which may undertake nucleophilic attacks. Subsequently, the interaction of atomic oxygen with Pdn clusters was systematically studied, accounting for different possible anchoring positions. The hollow site was revealed to be the most favourable one. The increase in number of Pd atoms favoured higher spin states. Pd6O was identified as the most oxidised and energetically stable cluster. The calculated binding energy value of oxygen (3.5 eV) was in agreement with the Temperature Programmed Desorption (TPD) experimental results conducted on Pd(1 1 0) single-crystal surface. The NBO analysis evidenced that the occupancy of 2 s (2p) orbital of O decreased (increased) as the number of Pd atom increased. The negatively charged Pd atoms had a larger population of 4d orbitals than the neutral or positively charged ones. The interactions between O and Pd atoms were dominated by d-type orbitals.

Secondary electron emission behavior of nanostructured fluorocarbon film

Based on the theoretical analysis of secondary electron emission (SEE) behavior of semiconductor and insulator, this paper numerically calculates electron affinity (EA) and energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of fluorocarbon (FC) films with the variation of fluorine to carbon (F/C) ratio. As fluorine element exhibits strong electronegativity, the LUMO energy decreases and the EA increases with the incremental content of fluorine. Increasing F/C ratio contributes to stronger electron capture capacity. SEE behavior is mainly affected by the chemical compositions and island-like nanostructure of FC films. Based on the dynamic scaling theory, the growth process is divided into two stages, in which roughening and smoothing effects play the dominant role, respectively. Growth index of the two stages are 0.57±0.01 and 0.10±0.01. Prolonging sputtering time contributes to higher film thickness, bigger surface roughness and larger F/C ratio. Experimental results confirm that secondary electron emission yield (SEY) decreases from 3.02 to 1.60, as film thickness increases from 19 to 113 nm. After 7 days and 60 days aging, the highest incremental δmax is 3.68% and the largest reduced E1 is 11.11%. The SEE behavior of FC film is relatively stable in the atmosphere.

New insights to build Na+/vacancy disordering for high-performance P2-type layered oxide cathodes

P2-type Na-based layered oxides are potential cathode materials for high power Na-ion batteries (NIBs). However, complex Na+/vacancy ordering rearrangement evidenced by obvious voltage plateaus in the electrochemical profiles severely affects the Na storage capacities and cycling stability, hindering the commercialization of P2 materials. Herein, we show that the unfavorable rearrangement can be avoided by pre-forming lower Na content P2 materials with a delocalized electronic structure and modulated site energy difference between Naf and Nae, as demonstrated by DFT calculations. The disordered framework and enlarged interlayer spacing can be sustained throughout the whole electrochemical process, ensuring both a wider solid-solution region and smaller volume change during de-/sodiation. As a consequence, an excellent electrochemical performance, namely a high reversible capacity of 165.1 mAh g−1, a superior rate performance of 76.7% of capacity retention at 1000 mA g−1, and 91.7% capacity retention after 150 cycles, is harvested. Moreover, this strategy is universal and can be used to synthesize various disordering high-capacity P2 materials. This work provides a long-neglected and unexpected idea for improving the comprehensive performance of P2-type materials for facilitating their practical applications in NIBs.

Multiscale Study of the Charge Transport Properties of Silicone Rubber Oligomers.

Polymer dielectrics are widely used as insulation in electronic and electrical equipment. The charge transport process in polymer dielectrics under a high electric field, which is considered to result in electrical aging and even breakdown of equipment insulation, has attracted considerable attention. Based on a localized charge transfer model, the charge transport mechanism for typical silicone rubber (SR) insulating materials was studied by multiscale methods. A model of silicone rubber oligomers under standard conditions was generated by classical molecular dynamics. The frontier molecular orbitals and projected density of states for the SR oligomer were obtained via quantum chemistry methods. The electronic coupling, reorganization energy, and free energy difference for both electron and hole transfer processes between adjacent SR molecules in the molecular dynamics model were calculated. Both hole transfer and electron transfer in SR conform to an intermolecular hopping mechanism due to their high intramolecular reorganization energy and low intermolecular electronic coupling. The results of normal mode analysis for reorganization energy indicate that the high-temperature approximation holds for charge transport in SR around or above room temperature. The charge transfer trajectory and charge mobility in SR were simulated based on kinetic Monte Carlo simulations. The hole and electron mobilities at room temperature were calculated to be 7.24 × 10-11 and 2.76 × 10-9 cm2/Vs, respectively, which agrees with the experimental data. Both electron transport and hole transport in SR show thermal activation characteristics, with corresponding activation energies of 358 and 314 meV, respectively. This work suggests a physical model to describe the charge transport process in SR polymer dielectrics.

Long-Range Electron Tunneling from the Primary to Secondary Quinones in Photosystem II Enhanced by Hydrogen Bonds with a Nonheme Fe Complex.

The mechanisms governing the long-range electron tunneling from the primary (QA) to secondary (QB) quinones in photosystem II are clarified by analyzing superexchange pathways through a nonheme Fe complex, using a quantum mechanics/molecular mechanics/polarizable continuum model approach. The electron tunneling rate is evaluated using the Marcus-Levich-Jortner theory considering electronic coupling, energy difference, and Franck-Condon factor. The superexchange QA → QB electron tunneling is enhanced by hybridized σ/σ* orbitals of histidines (D2-His214 and D1-His215) via penetration of the wave function into hydrogen bonds with both QA and QB. Despite a large energy gap to the intermediate states, the contributions of the histidine σ/σ* orbitals to the superexchange coupling are larger than those of π/π* orbitals. Fe2+ is not an essential component for the QA → QB electron tunneling because hybridized histidine molecular orbitals can be coupled with both QA and QB simultaneously in the absence of Fe d orbitals.

First principles details into the grafting of aryl radicals onto the free-standing and borophene/Ag(1 1 1) surfaces

We suspect that a possible interaction of the aryl radicals with the borophene surface is important for the stabilization and functionalization of the surface. Therefore, the grafting of aryl radical onto the borophene film is investigated using first-principles calculations based on density functional theory. The binding energy of the phenyl radicals on the borophene sheet, population analysis, and electron energy difference studies indicate a covalent nature of the bond between the B atom of the borophene and the C atom of the phenyl radical. Electron localization function analysis (ELF) is applied to estimate the nature of the bond between the borophene and the grafted phenyl moiety. The Mulliken charge population is used to evaluate the possible electron transfer at the bond-forming atoms (B and C) during this process. The obtained results helped to shed light on the grafting mechanism, activation energy, stabilization, and nature of the formed chemical bond between borophene and para-substituted phenyl moieties.

Decomposition pathway of C4F7N gas considering the participation of ions

Recently, fluoronitrile C4F7N is regarded as a promising alternative gas for SF6, and its global warming potential (GWP) is extremely high. C4F7N has good insulation properties and a relatively low GWP, so it can be used as an insulation medium for gas-insulated switchgears. Some studies have been conducted on the decomposition pathway of C4F7N gas that may produce possible neutral molecules and free radicals, which helps understand the thermal decomposition of C4F7N. However, anions and cations will be produced under discharge conditions. In these cases, the decomposition pathway of C4F7N will be different. In this paper, the ionization decomposition pathway and the attachment decomposition pathway of C4F7N were first calculated, while the recombination processes of the cations and anions were also considered. The results can reveal the decomposition mechanism of C4F7N and the recombination mechanism of the stable products under discharge conditions. The energy changes of all the reactions were calculated, which reveals the difficulty of chemical reactions. To better investigate the formation mechanism of stable products, the partial discharge experiment was also carried out, and the decomposition products of C4F7N mixed gas were detected. Finally, the ionization energy and electron affinity energy of the stable products were also calculated, which can determine the difference in the total electronic energy between the neutral molecule and the ion. The results provide an important reference for studying the decomposition characteristics of C4F7N gas under discharge conditions from the theoretical aspect.

Bioinspired chlorine-resistant tailoring for polyamide reverse osmosis membrane based on tandem oxidation of natural α-lipoic acid on the surface

Active chlorine-vulnerability is the Achilles' heel for polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes during water desalination and/or purification. Chlorination disrupts the delicate PA skin layer on porous support, resulting in significantly deteriorative membrane permselectivity and rising maintenance cost. Inspired by the superior antioxidative capacity of biologically endogenous α-lipoic acid (LA), this work was dedicated to tailoring a chlorine-resistant RO membrane with LA sacrificial unit on the surface. It was evidenced that the characteristic dithiolane within LA preferentially reacted with active chlorine in feedwater, and the intimal PA selective layer was thus safeguarded from chlorine-triggered oxidation. The modifier was pre-assembled with LA and polyethylenimine (PEI) as the mediator, subsequently tethered onto membrane surface via one-step chemical coupling without any catalysts. A pretty balance between membrane permselectivity and grafted modifier amount was achieved via regulating the modifier concentration. The modified membrane exhibited significantly ameliorative chlorine-resistance relative to the pristine one, with normalized salt rejection still remained (99.3 ± 0.6)% and only (17 ± 5)% final flux loss after a rigorous static chlorine exposure of 8000 ppm·h under acidic condition (confidence level, P = 95%). The electronic energy differences of chlorination-involved chemical procedures were determined by density functional theory (DFT) calculation, and an energy-favored three-stage tandem oxidation mechanism of LA moiety was proposed. Accordingly, up to 5 equiv. of active chlorine can be captured by a single sacrificial unit. Such intrinsically high chlorine-consumption efficacy of LA-based sacrificial layer would retard the chlorination saturation that commonly invalidates sacrificial layers. This bioinspired work shed light on a novel, facile, and effective anti-chlorine strategy for PA-TFC RO membrane to maintain the stability of service performance.

Theoretical Study of Radical-Molecule Reactions with Negative Activation Energies in Combustion: Hydroxyl Radical Addition to Alkenes.

Many of the radical–molecule reactions are nonelementary reactions with negative activation energies, which usually proceed through two steps. They exist extensively in the atmospheric chemistry and hydrocarbon fuel combustion, so they are extensively studied both theoretically and experimentally. At the same time, various models, such as a two transition state model, a steady-state model, an equilibrium-state model, and a direct elementary dynamics model are proposed to get the kinetic parameters for the overall reaction. In this paper, a conversion temperature TC1 is defined as the temperature at which the standard molar Gibbs free energy change of the formation of the reaction complex is equal to zero, and it is found that when T ≫ TC1, the direct elementary dynamics model with an inclusion of the tunneling correction of the second step reaction is applicable to calculate the overall reaction rate constants for this kind of reaction system. The reaction class of hydroxyl radical addition to alkenes is chosen as the objects of this study, five reactions are chosen as the representative for the reaction class, and their single-point energies are calculated using the method of CCSD(T)/CBS, and it is shown that the highest conversion temperature for the five reactions is 139.89 K, far below the usual initial low-temperature (550 K) oxidation chemistry of hydrocarbon fuels; therefore, the steady-state approximation method is applicable. All geometry optimizations are performed at the BH&HLYP/6-311+G(d,p) level, and the result shows that the geometric parameters in the reaction centers are conserved; hence, the isodesmic reaction method is applicable to this reaction class. To validate the accuracy of this scheme, a comparison of electronic energy difference at the BH&HLYP/6-311+G(d,p) level and the corrected electronic energy difference with the electronic energy difference at the CCSD(T)/CBS level is performed for the five representative reactions, and it is shown that the maximum absolute deviation of electronic energy difference can be reduced from 2.54 kcal·mol–1 before correction to 0.58 kcal·mol–1 after correction, indicating that the isodesmic reaction method is applicable for the accurate calculation of the kinetic parameters for large-size molecular systems with a negative activation energy reaction. The overall rate constants for 44 reactions of the reaction class of hydroxyl radical addition to alkenes are calculated using the transition-state theory in combination with the isodesmic correction scheme, and high-pressure limit rate rules for the reaction class are developed. In addition, the thermodynamic parameter is calculated and the results indicate that our dynamics model is applicable for our studied reaction class. A chemical kinetic modeling and sensitivity analysis using the calculated kinetic data is performed for the combustion of ethene, and the results indicate the studied reaction is important for the low-to-medium temperature combustion modeling of ethene.

Hydrogen bonding of dimethylpyridine clusters in water: Correlation between the lower consolute solution temperature and electron interaction energy

We examine the ordering of the Lower Consolute Solution Temperatures (LCSTs) for a set of dimethylpyridines. Density functional theory (DFT) is used. The equilibrium geometries and binding energies of dimers, each comprised of a pair of dimethylpyridines in a sandwich conformation and one H2O molecule at a pivotal site between the nitrogens (the 2:1 dimer), are calculated. It was shown previously that dimer formation in the water-rich zone of the phase diagram has a crucial role in dimethylpyridine demixing. In the resulting dimer diffusion, large hydrophobic clusters of mostly organic content, which expel water and promote phase separation, are assembled. In this description, phase separation requires the formation of 2:1 dimers, but it is the cleavage of hydrogen bonds of the neighboring H2O molecules, which stimulates the diffusion and the subsequent separation dynamics at the LCST. In the present study, we investigate this model and calculate the interaction strength of the external hydrogen bonds. This is obtained as the difference in electronic energy between the 2:1 dimer and the dimer augmented by one or two H2O molecules. The results are compared to the known LCST hierarchy in five dimethylpyridines (DMP): 2,6-DMP > 2,4-DMP > 2,5-DMP > 3,4-DMP > 3,5-DMP. The complexes are derived using high level Kohn-Sham DFT including dispersion terms. The hydrophobic-hydrophilic properties are accounted for by the solvation model, employed for the mixed medium of 60%-water and 40%-organic content. This is simulated by combination of model descriptors of water and DMP in the parameterization scheme of the polarizable continuum model. The calculation results agree with the experimental evidence.

Synthesis, crystal structure and conformational analysis of an unexpected [1,5]dithiocine product of aminopyridine and thiovanillin.

The condensation reaction of 2-mercapto-3-methoxybenzaldehyde with 3-aminopyridine afforded an unexpected N-alkylated [1,5]dithiocine instead of the N-salicylideneaniline. The proposed mechanism for this condensation involves a strong intramolecular hydrogen bond between the thiol and the amine groups, leading to a second condensation. The corresponding product, i.e. 4,10-dimethoxy-13-(pyridin-3-yl)-6H,12H-6,12-epiminodibenzo[b,f][1,5]dithiocine methanol 0.463-solvate, C21H18N2O2S2·0.463CH3OH, was characterized by single-crystal X-ray diffraction analysis. The supramolecular structure shows π-π stacking and S...S interactions in the crystal packing. Within the asymmetric unit, two geometries of the N atom are observed. Although a planar geometry should be expected, a pyramidal one is observed due to the crystal packing. The presence of the two geometries was further supported by density functional theory (DFT) calculations that show an electronic energy difference of less than 2 kJ mol-1 between the two conformers.

Modelling the enthalpy change and transition temperature dependence of the metal-insulator transition in pure and doped vanadium dioxide.

We compare various calculation methods to determine the electronic structures and energy differences of the phases of VO2. We show that density functional methods in the form of GGA+U are able to describe the enthalpy difference (latent heat) between the rutile and M1 phases of VO2, and the effect of doping on the transition temperature and on the band gap of the M1 phase. An enthalpy difference of ΔE0 = -44.2 meV per formula unit, similar to the experimental value, is obtained if the randomly oriented spins of the paramagnetic rutile phase are treated by a non-collinear spin density functional calculation. The predicted change in the transition temperature of VO2 for Ge, Si or Mg doping is calculated and is in good agreement with the experiment data.

The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need to be taken into account for a reliable description. Among the different contributions, the zero-point energy (ZPE) and the entropy play key roles. These quantities are usually calculated assuming a harmonic oscillator model for the molecular vibrations. We investigated the impact of including anharmonic corrections on the ZPE and the entropy and indirectly on the critical temperature of spin crossover. As test systems, we used a set of ten Fe(II) complexes and one Fe(III) complex, covering different coordination modes (mono-, bi-, and tri-dentate ligands), decreasing coordination number upon spin crossover, coordination by second- and third-row atoms, and changes in the oxidation state. The results show that the anharmonicity has a measurable effect, but it is in general rather small, and tendencies are not easily recognized. As a conclusion, we put forward that for high precision results, one should be aware of the anharmonic effects, but as long as computational chemistry is still struggling with other larger factors like the influence of the environment and the accurate determination of the electronic energy difference between HS and LS, the anharmonicity of the vibrational modes is a minor concern.

DFT-based study on H2S and SOF2 adsorption on Si-MoS2 monolayer

H2S and SOF2 gas are two typical decomposition products of SF6 gas under partial discharge condition. Based on the density functional theory (DFT), several doping structures of Si-MoS2 and adsorption structures of gas adsorbed Si-MoS2 were investigated. The electronic property, adsorption energy, charge transfer, and electron density difference were calculated to analyze the adsorption mechanism. Compared with the structure of pristine MoS2 monolayer, Si doping improves the surface activity of MoS2 monolayer. Moreover, the introduction of Si atom increases the effects of orbital hybridization between gas molecules and MoS2 monolayer, and promotes the charge transfer. Especially, SOF2 possesses a large adsorption energy with Si-MoS2 by crossing a small energy barrier. In addition, the good compatibility of Si-MoS2 with SF6 atmosphere, makes it a promising adsorbent for SF6 decomposition products removal.

Gas-Phase Ozone Reactions with a Structurally Diverse Set of Molecules: Barrier Heights and Reaction Energies Evaluated by Coupled Cluster and Density Functional Theory Calculations.

Reactions with ozone transform organic and inorganic molecules in water treatment systems as well as in atmospheric chemistry, either in the aqueous phase, at gas/particle interfaces, or in the gas phase. Computed thermokinetic data can be used to estimate the reactivities of molecules toward ozone in cases where no experimental data are available. Although the gas-phase reactivity of olefins with ozone has been characterized extensively in the literature, this is not the case for the richer chemistry of ozone with polar molecules, which occurs in the aqueous phase or in microhydrated environments. Here, we selected a number of model reactions with small molecules (ethene, ethyne, hydrogen cyanide, hydrogen chloride, ammonia, bromide, and trimethylamine) to study the accuracy of different quantum chemical methods for describing the reactivities of these molecules with ozone. We calculated benchmark electronic energies of gas-phase reactions of these systems with single-reference coupled cluster (CC) theory. These benchmark results for the binding energy in the van der Waals complex, the energy of the transition structure, and the reaction energy were estimated to be accurate within 1-2 kcal mol-1. Singlet oxygen (1O2) is a common product of ozone reactions. Coupled cluster calculations with up to perturbative quadruples (CCSDT( Q)) were needed to obtain reaction energies accurate within 1 kcal mol-1 when this species was involved. In (micro)hydrated environments or at interfaces, coupled cluster methods are prohibitively expensive in most cases. We tested the suitability of some contemporary density functional theory (DFT) methods to reproduce the benchmark electronic energy differences. Range-separated functionals were found to be promising candidates to estimate forward barrier heights, with LC-ωPBE rivaling the accuracy of CCSD( T). For energies of reaction, however, DFT methods exhibited large systematic errors, depending on their fraction of orbital exchange. This was found to worsen when 1O2 is a product, and no safe recommendation can be given for DFT reaction energies in such cases.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer.

Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a purely electronic excitonic coupling model. Energy transfer can leave excess energy behind as vibration on the electronic ground state of the donor, allowing vibrational relaxation on the donor's ground electronic state to make energy transfer permanent by removing excess energy from the excited electronic state of the dimer.