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Prediction of redox potentials is essential for catalysis and energy storage. Although density functional theory (DFT) calculations have enabled rapid redox potential predictions for numerous compounds, prominent errors persist compared to experimental measurements. In this work, we develop machine learning (ML) models to reduce the errors of redox potential calculations in both implicit and explicit solvent models. Training and testing of the ML correction models are based on the diverse ROP313 dataset with experimental redox potentials measured for organic and organometallic compounds in a variety of solvents. For the implicit solvent approach, our ML models can reduce both the systematic bias and the number of outliers. ML corrected redox potentials also demonstrate less sensitivity to DFT functional choice. For the explicit solvent approach, we significantly reduce the computational costs by embedding the microsolvated cluster in implicit bulk solvent, obtaining converged redox potential results with a smaller solvation shell. This combined implicit-explicit solvent model, together with GPU-accelerated quantum chemistry methods, enabled rapid generation of a large dataset of explicit-solvent-calculated redox potentials for 165 organic compounds, allowing detailed investigation of the error sources in explicit solvent redox potential calculations.

Two novel 3-D Ln(III)–Cu(I) heterometallic coordination polymers, [Ln2Cu2(L3)4(C2O4)2]·H2O (Ln = Sm, Eu; HL3 = 5-aminonicotinic acid), were hydrothermally produced by reacting lanthanide oxide and copper halide with 5-aminonicotinic acid and orotic acid. In the two isostructural complexes, {Ln6}-wheel clusters link each other via edge-sharing mode, constructing honeycomb-like layers which stack in –ABAB– mode. On the whole, the architectures can be described as sandwich framework constructed by {Ln6}-wheel layers pillared by interlamellar [CuOL32] triangle pillars. The electronic structure was theoretically calculated by the density functional theory, confirming the direct transition character. The steady and transient photoluminescent spectra were measured, from which the intensity parameters, radiative lifetime and quantum efficiency were calculated within the framework of the Judd–Ofelt theory. [Eu2Cu2(L3)4(C2O4)2]·H2O can be regarded as a potential candidate for LED applications.

Despite its widespread use in chemical discovery, approximate density functional theory (DFT) is poorly suited to many targets, such as those containing open-shell, 3d transition metals that can be expected to have strong multireference (MR) character. For discovery workflows to be predictive, we need automated, low-cost methods that can distinguish the regions of chemical space where DFT should be applied from those where it should not. We curate more than 4800 open-shell transition-metal complexes up to hundreds of atoms in size from prior high-throughput DFT studies and evaluate affordable, finite-temperature DFT fractional occupation number (FON)-based MR diagnostics. We show that intuitive measures of strong correlation (i.e., the HOMO-LUMO gap) are not predictive of MR character as judged by FON-based diagnostics. Analysis of independently trained machine learning (ML) models to predict HOMO-LUMO gaps and FON-based diagnostics reveals differences in the metal and ligand sensitivity of the two quantities. We use our trained ML models to rapidly evaluate MR character over a space of ∼187000 theoretical complexes, identifying large-scale trends in spin-state-dependent MR character and finding small HOMO-LUMO gap complexes while ensuring low MR character.

Huisgen's 1960 announcement of the concept of 1,3-dipolar cycloadditions was published the year before Alder's study of the reaction of diazomethane and dimethylfulvene. The diazomethane reaction was studied again in 1970 by Houk et al. and shown to give a [6+4] adduct. Padwa's nitrile ylide cycloaddition to dimethylfulvene (1978) gave [6+4] and [4+2] adducts. We performed computational studies of these reactions with density functional theory (DFT) and show that they involve ambimodal [6+4]/[4+2] transition states that can lead to either type of cycloadduct from one transition state. We dedicate this paper to the extraordinary life and humanity of Rolf Huisgen, and to the undying influence of his discoveries on chemistry.

Focusing on renewable energy, we are devoted to developping efficient, robust and low cost water reduction catalysts (WRCs). Two new Cu-based borate catalysts, namely H2Na2K2[(μ4-O)Cu4@B20O32(OH)8]·21H2O (1) and H2Rb1.6K2.4[(μ4-O)Cu4@B20O32 (OH)8]·15H2O (2), with cubic supramolecular cages were synthesized under a hydrothermal condition. Moreover, new copper complexes were applied as water reduction catalysts (WRCs) in the presence of [Ir(ppy)2(dtbbpy)][PF6] as photosensitizer and triethanolamine (TEOA) as the sacrificial electron donor. Nevertheless, the main active place is attributed to the centre of Borates [(μ4-O)Cu4@B20O32(OH)8], and the atomic radius of the counter cation would be the critical factor of the photocatalytic activity. Increasing the atomic radius from the Na atom to the Rb atom, causes the photocatalytic activity to decrease efficiently. The experimental results match well with the density functional theory (DFT) conclusion. It is noteworthy to mention that our research not only enriches the Cu-based borate chemistry, but also investigates the photocatalytic activity of Cu-based borates. This would guide us through the borate synthesis and to develop their applications toward energy and the environment.

Pressure plays essential roles in chemistry by altering structures and controlling chemical reactions. The extreme-pressure polarizable continuum model (XP-PCM) is an emerging method with an efficient quantum mechanical description of small- and medium-sized molecules at high pressure (on the order of GPa). However, its application to large molecular systems was previously hampered by a CPU computation bottleneck: the Pauli repulsion potential unique to XP-PCM requires the evaluation of a large number of electric field integrals, resulting in significant computational overhead compared to the gas-phase or standard-pressure polarizable continuum model calculations. Here, we exploit advances in graphical processing units (GPUs) to accelerate the XP-PCM-integral evaluations. This enables high-pressure quantum chemistry simulation of proteins that used to be computationally intractable. We benchmarked the performance using 18 small proteins in aqueous solutions. Using a single GPU, our method evaluates the XP-PCM free energy of a protein with over 500 atoms and 4000 basis functions within half an hour. The time taken by the XP-PCM-integral evaluation is typically 1% of the time taken for a gas-phase density functional theory (DFT) on the same system. The overall XP-PCM calculations require less computational effort than that for their gas-phase counterpart due to the improved convergence of self-consistent field iterations. Therefore, the description of the high-pressure effects with our GPU-accelerated XP-PCM is feasible for any molecule tractable for gas-phase DFT calculation. We have also validated the accuracy of our method on small molecules whose properties under high pressure are known from experiments or previous theoretical studies.

Accelerated discovery with machine learning (ML) has begun to provide the advances in efficiency needed to overcome the combinatorial challenge of computational materials design. Nevertheless, ML-accelerated discovery both inherits the biases of training data derived from density functional theory (DFT) and leads to many attempted calculations that are doomed to fail. Many compelling functional materials and catalytic processes involve strained chemical bonds, open-shell radicals and diradicals, or metal-organic bonds to open-shell transition-metal centers. Although promising targets, these materials present unique challenges for electronic structure methods and combinatorial challenges for their discovery. In this Perspective, we describe the advances needed in accuracy, efficiency, and approach beyond what is typical in conventional DFT-based ML workflows. These challenges have begun to be addressed through ML models trained to predict the results of multiple methods or the differences between them, enabling quantitative sensitivity analysis. For DFT to be trusted for a given data point in a high-throughput screen, it must pass a series of tests. ML models that predict the likelihood of calculation success and detect the presence of strong correlation will enable rapid diagnoses and adaptation strategies. These "decision engines" represent the first steps toward autonomous workflows that avoid the need for expert determination of the robustness of DFT-based materials discoveries.

The conversion of light energy into work is essential to life on earth. Bacteriorhodopsin (bR), a light-activated proton pump in Archae, has served for many years as a model system for the study of...

Magnetic ferroferric oxide-supported bimetallic Pd-In cluster sub-nanoparticles were used for the first time for the catalytic reduction of nitrates. Due to the unique properties of the FeOx support, the PdIn active centers could be highly dispersed in both nano- and sub-nanoscales. A variety of characterizations and the charge density difference model confirm that a strong metal-support interaction exists between the active sites and the support. The PdIn nanoparticles on FeOx show high selectivity toward nitrogen and excellent cyclic activity due to ferromagnetism, which broaden its prospect in practical water treatment. Moreover, the active centers in the sub-nanoscale are used in the nitrate reduction process for the first time and they show a distinct higher activity in denitration. The rate constant for nitrate conversion on PdIn sub-nanoparticles is larger than that for its nanometer counterpart based on the Langmuir-Hinshelwood model. High turnover frequency value and ammonia selectivity are achieved for the small-sized sub-nanocatalyst. The FeOx-supported PdIn nanoparticles and sub-nanoparticles have two application areas in water purification and ammonia recovery, respectively. Density functional theory calculations on the adsorption energies of elemental reactions are also performed, which shed some light on the catalysis mechanism and catalyst design.

In this work, the aromatic hydroxylation mechanism of the [Cu2(H-XYL)O2]2+ complex mediated by a peroxo dicopper core and Cu-ligand effects are investigated by using hybrid density functional theory (DFT) and the broken symmetry B3LYP method. Based on the calculated free-energy profiles, we proposed two available mechanisms. The first reaction steps of both mechanisms involve concerted O–O bond cleavage and C–O bond formation and the second step involves the Wagner–Meerwein rearrangement of the substrate by a [1,2] H shift (HA shift from CA to CC) or (HA shift from CA to OA) across the phenyl ring to form stable dienone intermediates, and this is followed by the protonation of bridging oxygen atoms to produce the final hydroxylated dicopper(II) product. The HA shift from CA to CC mechanism is the energetically most favorable, in which the first reaction step is the rate-limiting reaction, with a calculated free-energy barrier of 19.0 kcal mol−1 and a deuterium kinetic isotope effect of 1.0, in agreement with experimental observations. The calculation also shows that the reaction started from the P-type species of [Cu2(H-XYL)O2]2+ which is capable of mediating the direct hydroxylation of aromatic substrates without the intermediacy of an O-type species. Finally, we designed some new complexes with different Cu-ligands and found the complex that computationally possesses a higher activity in mediating the hydroxylation of the ligand based aromatic substrate; here, Cu loses a pyridyl ligand donor by dissociation, compared to the [Cu2(H-XYL)O2]2+ complex.

Conical intersections control excited state reactivity, and thus, elucidating and predicting their geometric and energetic characteristics are crucial for understanding photochemistry. Locating these intersections requires accurate and efficient electronic structure methods. Unfortunately, the most accurate methods (e.g., multireference perturbation theories such as XMS-CASPT2) are computationally challenging for large molecules. The state-interaction state-averaged restricted ensemble referenced Kohn-Sham (SI-SA-REKS) method is a computationally efficient alternative. The application of SI-SA-REKS to photochemistry was previously hampered by a lack of analytical nuclear gradients and nonadiabatic coupling matrix elements. We have recently derived analytical energy derivatives for the SI-SA-REKS method and implemented the method effectively on graphical processing units. We demonstrate that our implementation gives the correct conical intersection topography and energetics for several examples. Furthermore, our implementation of SI-SA-REKS is computationally efficient, with observed sub-quadratic scaling as a function of molecular size. This demonstrates the promise of SI-SA-REKS for excited state dynamics of large molecular systems.

The nucleophile-intercepted Beckmann fragmentation (NuBFr) has the potential to be broadly applicable to the synthesis of indoline alkaloid based natural products. However, the reaction has not been widely adopted, in part, because of limitations associated with the availability of appropriate promoter–Nu reagents. We have devised a stereospecific Ag(I)-promoted reaction for functionalizing NuBFr products to give novel compositions-of-matter that may be useful in synthesis and medicinal chemistry. With unhindered amine nucleophiles, structurally unique [2.2.2]-bicycloamidines are generated. We also disclose for the first time detailed density functional theory (DFT) studies which shed light on the mechanism of the NuBFr and Ag-promoted substitution reaction that supports an unusual aziridinium ion as a key intermediate.

High-throughput computational screening typically employs methods (i.e., density functional theory or DFT) that can fail to describe challenging molecules, such as those with strongly correlated electronic structure. In such cases, multireference (MR) correlated wavefunction theory (WFT) would be the appropriate choice but remains more challenging to carry out and automate than single-reference (SR) WFT or DFT. Numerous diagnostics have been proposed for identifying when MR character is likely to have an effect on the predictive power of SR calculations, but conflicting conclusions about diagnostic performance have been reached on small data sets. We compute 15 MR diagnostics, ranging from affordable DFT-based to more costly MR-WFT-based diagnostics, on a set of 3,165 equilibrium and distorted small organic molecules containing up to six heavy atoms. Conflicting MR character assignments and low pairwise linear correlations among diagnostics are also observed over this set. We evaluate the ability of existing diagnostics to predict the percent recovery of the correlation energy, %Ecorr. None of the DFT-based diagnostics are nearly as predictive of %Ecorr as the best WFT-based diagnostics. To overcome the limitation of this cost–accuracy trade-off, we develop machine learning (ML, i.e., kernel ridge regression) models to predict WFT-based diagnostics from a combination of DFT-based diagnostics and a new, size-independent 3D geometric representation. The ML-predicted diagnostics correlate as well with MR effects as their computed (i.e., with WFT) values, significantly improving over the DFT-based diagnostics on which the models were trained. These ML models thus provide a promising approach to improve upon DFT-based diagnostic accuracy while remaining suitably low cost for high-throughput screening.

Copyright © 2020 American Chemical Society. High-throughput computational screening typically employs methods (i.e., density functional theory or DFT) that can fail to describe challenging molecules, such as those with strongly correlated electronic structure. In such cases, multireference (MR) correlated wavefunction theory (WFT) would be the appropriate choice but remains more challenging to carry out and automate than single-reference (SR) WFT or DFT. Numerous diagnostics have been proposed for identifying when MR character is likely to have an effect on the predictive power of SR calculations, but conflicting conclusions about diagnostic performance have been reached on small data sets. We compute 15 MR diagnostics, ranging from affordable DFT-based to more costly MR-WFT-based diagnostics, on a set of 3165 equilibrium and distorted small organic molecules containing up to six heavy atoms. Conflicting MR character assignments and low pairwise linear correlations among diagnostics are also observed over this set. We evaluate the ability of existing diagnostics to predict the percent recovery of the correlation energy, %Ecorr. None of the DFT-based diagnostics are nearly as predictive of %Ecorr as the best WFT-based diagnostics. To overcome the limitation of this cost-accuracy trade-off, we develop machine learning (ML, i.e., kernel ridge regression) models to predict WFT-based diagnostics from a combination of DFT-based diagnostics and a new, size-independent 3D geometric representation. The ML-predicted diagnostics correlate as well with MR effects as their computed (i.e., with WFT) values, significantly improving over the DFT-based diagnostics on which the models were trained. These ML models thus provide a promising approach to improve upon DFT-based diagnostic accuracy while remaining suitably low cost for high-throughput screening.

First-principles calculations based on the density function theory (DFT) are implemented to explore the effect of Ce doping on the electronic structure and optical properties of LaBr3 crystals using generalized gradient approximation (GGA) +U. And band structure, density of states and optical properties are discussed. Due to the transition of Ce3+ ion from 4f-orbital to 5d-orbital, the band gaps of LaBr3:Ce (0.63 eV) is narrower than that of LaBr3 (3.569 eV), which produce more visible light in the same range of irradiated energy. Otherwise, the absorption spectrum (15.6 μm-1) and reflection index (less than 12%) of LaBr3:Ce are smaller than LaBr3 (20 μm-1, less than 15%, respectively), leading to transmit more visible light. The research shows reason that Ce doping can improve the luminescence performance of LaBr3 scintillators and the results are compared with the available experimental data.

For over a century, the structures and reactivities of strained organic compounds have captivated the chemical community. Whereas triple-bond-containing strained intermediates have been well studied, cyclic allenes have received far less attention. Additionally, studies of cyclic allenes that bear heteroatoms in the ring are scarce. We report an experimental and computational study of azacyclic allenes, which features syntheses of stable allene precursors, the mild generation and Diels–Alder trapping of the desired cyclic allenes, and explanations of the observed regio- and diastereoselectivities. Furthermore, we show that stereochemical information can be transferred from an enantioenriched silyl triflate starting material to a Diels–Alder cycloadduct by way of a stereochemically defined azacyclic allene intermediate. These studies demonstrate that heteroatom-containing cyclic allenes, despite previously being overlooked as valuable synthetic intermediates, may be harnessed for the construction of complex molecular scaffolds bearing multiple stereogenic centres. Strained organic compounds have long fascinated the chemistry community. Heterocyclic allenes are particularly interesting strained intermediates, but their use in synthetic chemistry is rather scarce. Now, an experimental and computational study of azacyclic allenes demonstrates that heteroatom-containing cyclic allenes can be harnessed for the construction of complex molecular scaffolds, including those that bear multiple stereogenic centres.

The unexpected formation of a 4-hydroxytetrahydroquinolin-2(1H)-one from a bicyclo[3.3.1]nonanetrione system and an amino alcohol in the presence of TsOH is reported. The mechanism of this transformation was studied by DFT calculations. The reaction provides an entry to the synthesis of highly functionalized 4-hydroxytetrahydroquinolin-2(1H)-ones.

The acetate-based ionic liquids (ILs), e.g., [nBu4N]OAc, have been developed for challenging 4-electron reduction of CO2 with amines and hydrosilane to afford aminals. Notably, polymethylhydrosiloxane, a cheap byproduct of the silicone industry, also works well as a reductant. Furthermore, an alternative pathway is rationally proposed via thorough density functional theory (DFT) study. In addition, the ILs play a surprisingly significant role through decreasing activation free energy. More importantly, the essence of being kinetically favorable with 4-electron reduction and thermodynamically favorable with 6-electron reduction is unveiled by DFT study, which guides us to successfully get 6-electron reductive products of CO2, i.e., methylamine. This work represents upgrading usage of both carbon and silicon wastes to valuable chemicals via IL catalysis.

The electronic and crystal structural properties of Bi-doped Sr3Ti2O7 are studied using the first principles density functional theory (DFT) based on pseudopotentials basis and plane-wave method. Our results show that the formation energy of Bi doping in Site-1 and Site-2 of Sr3Ti2O7 increases with increasing doping concentration. And at the same doping concentration, the formation energy of Bi doping in Site-2 is lower than that in Site-1. The undoped Sr3Ti2O7 is found to be an insulator and its Fermi level stays at the top of the valence band. While the Fermi level of the Bi-doped Sr3Ti2O7 moves into the bottom of conduction band, the system undergoes an insulator-to-metal phase transition. Furthermore, our calculation results demonstrated that the Fermi level of the Bi-doped Sr3Ti2O7 goes deeper into the bottom of conduction band with increasing doping concentration.

Redox-active organic molecules have attracted much attention as alternatives to transition-metal-based electrodes for lithium-ion batteries due to their low cost and large abundance. However, the relatively low cycling stability still prevents some of the most promising molecules to be used as lithium-ion electrodes. Herein, we used 1,4,5,8-naphthalene diimide (NDI) as a model molecule to systematically investigate its intrinsic electrochemical property, including its electrolyte compatibility, maximum capacity, cycling stability, and rate capability in different organic electrolytes. Extensive physicochemical characterization, electrochemical measurement, and density function theory (DFT) calculation together show that the electrode–electrolyte interaction is the key factor determining its specific capacity and cycling stability. With a proper selection of electrolytes, NDI molecule, which was considered to be not stable for lithium storage, can achieve near theoretical capacity (based on two-electron re...

The activity of exposed crystal facets directly determines its physicochemical properties. Thus, acquiring a high percentage of reactive facets by crystal facet engineering is highly desirable for improving the catalytic reactivity. Herein, single-crystalline α-MnO2 nanowires with major exposed high-index {310} facets were synthesized via a facile hydrothermal route with the assistance of a capping agent of oxalate ions. Comparing with two other low-index facets ({100} and {110}), the resulting α-MnO2 nanowires with exposed {310} facets exhibited much better activity and stability for carcinogenic formaldehyde (HCHO) oxidation, making 100% of 100 ppm of HCHO mineralize into CO2 at 60 °C, even better than some Ag supported catalysts. The density functional theory (DFT) calculations were used to investigate the difference in the catalytic activity of α-MnO2 with exposed {100}, {110}, and {310} facets. The experimental characterization and theoretical calculations all confirm that the {310} facets with high ...

The pyrene systems are remarkable candidates for organic semiconductor materials. The theoretical investigation on electronic and transport properties of a series of pyrene derivatives has been carried out by quantum mechanics (QM) calculations combined with Marcus-Hush electron transfer theory and density functional theory (DFT). Various structure modifications of 12 different pypene derivative molecules are investigated to reveal structure-mobility relationships of the organic materials, such as introducing different substitution groups in different positions, changing the central core of the molecule by linking different backbone structure. The theoretical calculation results are in good agreement with the experimental results, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies. The reorganization energies and charge mobility are estimated based on molecule single-crystal structures and incoherent charge-hopping transfer model at 300 K. For designing high performance organic materials, the hole mobility is predicted to reach a high value of 2.95 cm 2 V −1 s −1 for compound 2,7-diphenyl-substituted derivative and the largest electron mobility for 4,5-dithienypyrene as 6.24 cm 2 V −1 s −1 , indicating that pyrene derivatives are promising candidates for organic semiconductors. The 3D simulation mobility figures are calculated step by step. In this study, the charge transport properties largely depend upon the packing mode of organic semiconducting molecules and the structural change of the substituent group. Our calculation results could provide enlightening information on possible methods to increase the charge mobility and the design for organic electronic devices with high-mobility.

For approximate density functional theory (DFT) to be useful in catalytic applications of transition metal complexes, modeling strategies must simultaneously address electronic, geometric, and energetic properties of the relevant species. We show that for representative transition metal triatomics (MO2, where M = Cr, Mn, Fe, Co, or Ni) and related diatomics the incorporation of Hartree–Fock (HF) exchange in most cases improves the properties of the Born–Oppenheimer potential energy surface (PES) with respect to accurate experimental or CCSD(T) references. We rationalize this observation by noting reduced delocalization obtained with hybrid functionals (20–40% HF exchange), as evidenced by reduced hybridization of non-bonding orbitals and increases in metal partial charges. Although we show that the optimal exchange fraction is both property and system specific, incorporating HF exchange synergistically improves properties of density, structure, and energetics within a single PES characterized by moderately covalent bonding. The same improvement is not observed in the ordering of MO2 spin states, as good agreement of semi-local DFT spin state ordering is worsened by over stabilization of higher spin states when HF exchange is added. More work is needed to understand minimal functional forms capable of improving multiple properties with respect to semi-local DFT descriptions of transition metal chemistry.

Density functional theory (DFT) is widely applied to both molecules and materials, but well known energetic delocalization and static correlation errors in practical exchange-correlation approximations limit quantitative accuracy. Common methods that correct energetic delocalization errors, such as the Hubbard U correction in DFT+U or Hartree-Fock exchange in global hybrids, do so at the cost of worsening static correlation errors. We recently introduced an alternate approach [Bajaj et al., J. Chem. Phys. 147, 191101 (2017)] known as judiciously modified DFT (jmDFT), wherein the deviation from exact behavior of semilocal functionals over both fractional spin and charge, i.e., the so-called flat plane, was used to motivate functional forms of second order analytic corrections. In this work, we introduce fully nonempirical expressions for all four coefficients in a DFT+U+J-inspired form of jmDFT, where all coefficients are obtained only from energies and eigenvalues of the integer-electron systems. We show good agreement for U and J coefficients obtained nonempirically as compared with the results of numerical fitting in a jmDFT U+J/J' correction. Incorporating the fully nonempirical jmDFT correction reduces and even eliminates the fractional spin error at the same time as eliminating the energetic delocalization error. We show that this approach extends beyond s-electron systems to higher angular momentum cases including p- and d-electrons. Finally, we diagnose some shortcomings of the current jmDFT approach that limit its ability to improve upon DFT results for cases such as weakly bound anions due to poor underlying semilocal functional behavior.

An efficient method for highly selective alkenyl C-P bond cleavage, enabled by organic dyes and visible-light irradiation, was developed. This novel protocol involves a highly regioselective radical pathway initiated by singlet oxygen, affording diverse alkynyl phosphinates with good-to-excellent yields. Mechanistic studies and density functional theory calculations suggested an intramolecular process involving phosphorus migration, instead of phosphorus radical formation, at the early stage of the reaction.

Single atom catalysts (SACs) are emergent catalytic materials that have the promise of merging the scalability of heterogeneous catalysts with the high activity and atom economy of homogeneous catalysts. Computational, first-principles modeling can provide essential insight into SAC mechanism and active site configuration, where the sub-nm-scale environment can challenge even the highest-resolution experimental spectroscopic techniques. Nevertheless, the very properties that make SACs attractive in catalysis, such as localized d electrons of the isolated transition metal center, make them challenging to study with conventional computational modeling using density functional theory (DFT). For example, Fe/N-doped graphitic SACs have exhibited spin-state dependent reactivity that remains poorly understood. However, spin-state ordering in DFT is very sensitive to the nature of the functional approximation chosen. In this work, we develop accurate benchmarks from correlated wavefunction theory (WFT) for relevant octahedral complexes. We use those benchmarks to evaluate optimal DFT functional choice for predicting spin state ordering in small octahedral complexes as well as models of pyridinic and pyrrolic nitrogen environments expected in larger SACs. Using these guidelines, we determine Fe/N-doped graphene SAC model properties and reactivity as well as their sensitivities to DFT functional choice. Finally, we conclude with broad recommendations for computational modeling of open-shell transition metal single-atom catalysts.

Amino-specified pyrazolium ionic liquid (APEPzBr) is synthesized by two steps. It is interesting that the product of the first step ([EPzPNH3]Br2) could also catalyze the coupling reaction of carbon dioxide (CO2) and epoxides under 70 °C along with 0.5 MPa CO2 pressure, which is even more benign than APEPzBr. It is attributed to the strong ability of [EPzPNH3]Br2 to absorb CO2 along with robust electrophilic activation, which is testified by density functional theory and 13C NMR measurement. The difference between [EPzPNH3]Br2 and APEPzBr is further elucidated by electron localization function (ELF) and atoms in molecules (AIM).

We compared superatomic orbitals mainly contributed by 6s atomic orbitals among spherical core–shell cluster Au13, hexagonal plane Au7 and a (5,5) nanotube segment Au35 through first-principles density functional theory calculations. The compatibility between geometry and orbital morphology influences both the presence and the energy level order of particular superatomic orbitals. Taking Au13 as a reference, which possesses a regular configuration of 1S 21P 61D 5, the hexagonal Au7 in 1S 21P 41D 1 lacks the 1P occupied superatomic orbital which is distributed out of the structural plane. Different from the nearly degenerated five occupied 1D orbitals in Au13, Au35 in 1S 21P 61D 101F 101G 61H 1 shows energy separations over 4.0 eV between split 1D regions and 1F regions according to the preference of tubular geometry to different orbital morphologies. The structural reliance of the electronic structure revealed by these typical building blocks might be informative for bottom-up design and fabrication of nanoscale devices based on a gold nanostructure and contributes to the variety and operability of nanoscale materials.

The single particle energies obtained in a Kohn-Sham density functional theory (DFT) calculation are generally known to be poor approximations to electron excitation energies that are measured in transport, tunneling and spectroscopic experiments such as photo-emission spectroscopy. The correction to these energies can be obtained from the poles of a single particle Green’s function derived from a many-body perturbation theory. From a computational perspective, the accuracy and efficiency of such an approach depends on how a self energy term that properly accounts for dynamic screening of electrons is approximated. The G0W0 approximation is a widely used technique in which the self energy is expressed as the convolution of a noninteracting Green’s function (G0) and a screened Coulomb interaction (W0) in the frequency domain. The computational cost associated with such a convolution is high due to the high complexity of evaluating W0 at multiple frequencies. In this paper, we discuss how the cost of G0W0 calculation can be reduced by constructing a low rank approximation to the frequency dependent part of W0. In particular, we examine the effect of such a low rank approximation on the accuracy of the G0W0 approximation. We also discuss how the numerical convolution of G0 and W0 can be evaluated efficiently and accurately by using a contour deformation technique with an appropriate choice of the contour.

The noncovalent halogen halogen (X X ) interaction, which shows significant anisotropic feature, is extensively used in rationally designing supramolecular assemblies. Here, beyond the binding energy of stable geometries, the anisotropic topology of the potential energy surface (PES) is explored. We show that most functionals of DFT give remarkably unphysical angular distortion of the PES. This is unlikely to be solved unless the components that ensure correct angular dependent behavior in the halogen bonding region are contained in the functionals. We also prove that simple empirical corrections may substantially quantify this unphysical angular distortion, and further investigation is recommended. These findings constitute a step forward toward the understanding of the nature of X X bonds , and provide some insights for the future designing of the state-of-art theoretical methods. (c) 2016 Wiley Periodicals, Inc.

The cycloadditions of benzene and ten different azabenzenes (pyridine, three diazines, three triazines, and three tetrazines) with the ethylene dienophile have been explored with density functional theory (M06-2X) and analyzed with the distortion/interaction model. Activation barriers correlate closely with both distortion energies and interaction energies over an activation energy range of 45 kcal/mol. The replacement of CH with N increases Diels-Alder reactivity due not only to the more favorable orbital interaction, but also to a decrease in distortion energy. The rates of reactions are greatly influenced by the nature of the bonds being formed: two C-C bonds > one C-C bond, and one C-N bond > two C-N bonds. The activation energy of Diels-Alder reactions correlates very well with reaction energies and with the NICS(0) values of the aromatic dienes. The distortion energy of the Diels-Alder reaction transition states mostly arises from the diene out-of-plane distortion energy.

PBEPBE-D3 calculations were performed to investigate how platinum (Pt) interacts with the internal and external surfaces of single-walled pristine, Si-, Ge-, and Sn-doped (6,6) carbon nanotubes (CNTs). Our calculations showed that atomic Pt demonstrates stronger binding strength on the external surfaces than the internal surface adsorption for the same type of nanotube. In cases of external surface adsorptions, Si-, Ge-, and Sn-doped CNTs show comparable binding energies for Pt, at least 1.40 eV larger than pristine CNT. This enhancement can be rationalized by the strong covalent interactions between Pt and XC (X = Si, Ge, and Sn) pairs based on structural and projected density of states analysis. In terms of internal surface adsorptions, Ge and Sn doping could significantly enhance the binding of Pt. Pt atom shows much more delocalized and bonding states inside Ge- and Sn-doped CNTs, indicating multiple-site interaction pattern when atomic Pt is confined inside the nanotubes. However, the internal surface of Si-doped CNT presents limited enhancement in Pt adsorption with respect to that of pristine CNT because of their similar binding geometries. © 2016 Wiley Periodicals, Inc.

A bifuncational catalytic system consisting of CaBr2 and 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) was developed for the efficient fixation of CO2 with epoxides to cyclic carbonates. Such a dual catalysis facilitates the reaction to proceed smoothly at atmospheric CO2 pressure, presumably due to the simultaneous activation of CO2 by DBU and epoxides by CaBr2. In addition, the activation role of CaBr2 was also studied using density functional theory (DFT) calculations. A plausible mechanism involving the DBU–CO2 adduct-assisted ring opening path and the bromide anion-promoted ring opening path is proposed, in combination with the activation of epoxides by the calcium cation. This process represents a simple, cost-effective and biocompatible route to obtain cyclic carbonates from CO2 under mild conditions, especially at atmospheric CO2 pressure.

Two dimensional (2D) materials such as metal carbides are attractive owing to their unique structures and various potential applications. Although various synthetic methods have been developed for fabrication of 2D materials, it is still challenging to directly synthesize 2D carbides. Herein, we propose a new approach to convert in-situ 3D iron carbide into defect free 2D one in conventional carbon steels by controlling the deformation accumulation to drive atomic rearrangement within the carbides. Density functional theory (DFT) calculation demonstrated that ring-like, helical and other morphological 2D iron carbides can be formed under 30 % compressive deformation. Experimentally, the strength of 2D hexagonal iron carbide is estimated to be 12 GPa–18 GPa, which is 4–5 times that of original orthorhombic iron carbide (3.0 GPa–3.5 GPa) and the in-situ grown 2D carbide results in 176 % increase in strength of the steels. The first principles simulations show that the 2D iron carbides can be converted through its multiple slip systems under both the compressive and tensile pressure. This approach may open a new door for in-situ controllable growth of various 2D materials owning to rich metallic bond variety, slip system multiplicity and deformation diversity in metallic alloys.

Ab initio pseudopotential total-energy calculations on infinite monatomic chains of Au are performed within density functional theory. We use the density functional perturbation theory to study the phonon spectra of these gold wires as a function of strain. Our results show that there does not seem to be a range of strain for which the linear chain is stable, contrary to what was stated by Ribeiro and Cohen [Phys. Rev. B 68 (2003) 035423]. For low strain, the zigzag chain is the stable geometry; while for higher strain, the chains with two or more aligned gold atoms are found to be more stable. At the limit between these two regimes, we predict a transition structure (an asymmetric zigzag chain) to be the most stable.

The structural, electrical and optical properties of four halogen elements F, Cl, Br, I doped phosphorene (X-phosphorene) were investigated by applying first principle calculations based on density functional theory. X-phosphorene have different bonding characters based on Mulliken population and differential charge analysis. The ionization energies of halogen atoms in X-phosphorene shown that F, Cl, Br are p-type dopants while I is n-type. In terms of the bandgap type, F-phosphorene and I-phosphorene are indirect, while Cl-phosphorene and Br-phosphorene are direct, besides, it is worth to note that Cl-phosphorene and I-phosphorene are promising spin-gapless semiconductors. All X-phosphorene show the anisotropic transport property after calculating its carrier effective masses based on obtained E-k relationship. The absorption abilities of X-phosphorene are increased in UV-A and UV-B regions, as well as in visible and infrared regions over against the intrinsic condition.

Pericyclic reactions are powerful transformations for the construction of carbon–carbon and carbon–heteroatom bonds in organic synthesis. Their role in biosynthesis is increasingly apparent, and mechanisms by which pericyclases can catalyse reactions are of major interest1. [4+2] cycloadditions (Diels–Alder reactions) have been widely used in organic synthesis2 for the formation of six-membered rings and are now well-established in biosynthesis3–6. [6+4] and other ‘higher-order’ cycloadditions were predicted7 in 1965, and are now increasingly common in the laboratory despite challenges arising from the generation of a highly strained ten-membered ring system8,9. However, although enzyme-catalysed [6+4] cycloadditions have been proposed10–12, they have not been proven to occur. Here we demonstrate a group of enzymes that catalyse a pericyclic [6+4] cycloaddition, which is a crucial step in the biosynthesis of streptoseomycin-type natural products. This type of pericyclase catalyses [6+4] and [4+2] cycloadditions through a single ambimodal transition state, which is consistent with previous proposals11,12. The [6+4] product is transformed to a less stable [4+2] adduct via a facile Cope rearrangement, and the [4+2] adduct is converted into the natural product enzymatically. Crystal structures of three pericyclases, computational simulations of potential energies and molecular dynamics, and site-directed mutagenesis establish the mechanism of this transformation. This work shows how enzymes are able to catalyse concerted pericyclic reactions involving ambimodal transition states. Enzymatic catalysis of pericyclic [6+4] cycloaddition reactions to form ten-membered rings is observed during biosynthesis of the macrocyclic antibiotic streptoseomycin, and the mechanism of these transformations is established.

We have comparatively investigated the adsorption behaviors of atomic platinum on the internal and external surfaces of single walled pristine and doped carbon nanotubes using density functional theory calculations. The equilibrium adsorption geometries, binding energy (Eb), and density of states of the Pt on these CNTs were calculated at the PBEPBE/LanL2DZ level. Our results reveal that the binding abilities of atomic Pt onto the internal and external surfaces of the CNTs are in following orders by dopant: O > Be > B > N > pristine. The binding energy of O–CNT towards atomic Pt more than doubles that of pristine CNT, which can be attributed to the active carbon sites created by C–O bond breaking, while N–CNT demonstrates the smallest enhancement due to its similar binding configuration for Pt with pristine CNT. In contrast, as a result of the confined space of nanotube, Pt has two more bonding sites inside the B– and Be–CNT, while the external counterparts prefer the double coordinated C–X bridge site. In this respect, Pt atom in Pt@X–CNT (X = B and Be) presents more delocalized and bonding states than Pt/X–CNT, though the binding energy of the former is smaller than the latter.

A series of acene-modified zinc-porphyrin dyes (benzene to pentacene, denoted as LAC-1 to LAC-5) were chosen to examine their performance as photosensitizers in dye-sensitized solar cells (DSSCs). Their structural, electronic, and optical properties were investigated at the DFT/TDDFT levels using various theoretical models (i.e., the gas phase model and the implicit/explicit solvent model). The dye@TiO2 complex was used to investigate the dye/semiconductor interfaces using both the cluster and periodic models. After a careful examination of the dependence of the results on different theoretical approaches, some basic principles could be derived based on the theoretical investigation of structure–function relationships in isolated dyes and dye–TiO2 assemblies. Based on these ideas, some general suggestions can be proposed for the future design of dyes for use in DSSCs. For instance, the DFT functionals used in estimating the critical parameters for DSSCs should be carefully validated. Sometimes the perform...

To achieve true blue-emitting iridium(III) complexes for organic light-emitting diodes, we theoretically designed a complex (dfbpy) 2 Ir(PˆN) ( 2 , PˆN = 5-(diphenylphosphinomethyl)-3-(trifluoromethyl)pyrazole), dfbpy = 2-(2,4-difluorobenzyl)-pyridine), which derived from its prototype complex (dfppy) 2 Ir(PˆN) ( 1 , dfppy : 2-(4,6-difluorophenyl)pyridine) by the insertion of methylene group between the pyridyl and phenyl segments. Then, their geometrical and electronic structure, absorption and emission were systematically and comparatively investigated using density functional theory calculations. It is found that the highest occupied molecular orbital (HOMO) (π component) of the functionalized complex 2 resides mainly on metal iridium atom and dfbpy ligand, whereas the lowest unoccupied molecular orbital (LUMO) is predominantly centered on π* orbital of cyclometalated dfbpy chelates. Our calculated results reveal the absorption at the 359 nm for 2 can be attributed to the mixture of M dπ L π*( dfbpy ) CT (metal-ligand charge transition, MLCT) and IL π(dfbpy) →π*(dfbpy) CT (intra-ligand charge transition, ILCT) transitions. In particular, the maxima emission for 2 is at 450 nm, which presents a blue shift up to 80 nm as compared to prototype complex 1 , indicating the introduction of methylene group is a feasible strategy to archive true blue-emitting materials.

Noncovalent interactions, such as hydrogen bonds and halogen bonds, are frequently used in drug designing and crystal engineering. Recently, a novel noncovalent pnicogen bonds have been identified as an important driving force in crystal structures with similar bonding mechanisms as hydrogen bond and halogen bond. Although the pnicogen bond is highly anisotropic, the pnicogen bond angles range from 160 degrees to 180 degrees due to the complicated substituent effects. To understand the anisotropic characters of pnicogen bond, a modification of the polarizable ellipsoidal force field (PEff) model previously used to define halogen bonds was proposed in this work. The potential energy surfaces (PESs) of mono- and polysubstituted PH3-NH3 complexes were calculated at CCSD(T), MP2, and density functional theory levels and were used to examine the modified PEff model. The results indicate that the modified PEff model can precisely characterize pnicogen bond. The root mean squared error of PES obtained with PEff model is less than 0.5 kcal/mol, compared with MP2 results. In addition, the modified PEff model may be applied to other noncovalent bond interactions, which is important to understand the role of intermolecular interactions in the self-assembly structures. (c) 2015 Wiley Periodicals, Inc.

The nonadiabatic dynamics of keto isocytosine in the gas phase has been investigated using the on-the-fly trajectory surface hopping method based on two electronic-structure methods: SA-CASSCF and ADC(2). The results estimate an excited-state lifetime of around 1000 fs at the SA-CASSCF level, while a much shorter lifetime of 250-350 fs is obtained at the ADC(2) level. Although three conical intersections (CIs) (Ethyl. I, Ethyl. II and C[double bond, length as m-dash]O stretching) are relevant to the nonadiabatic decay of keto isocytosine, their contributions to the nonadiabatic decay are highly dependent on the electronic-structure methods employed in the dynamics simulation. The Ethyl. II CI is the main channel in the dynamics simulations at the SA-CASSCF level, while the C[double bond, length as m-dash]O stretching CI becomes dominant at the ADC(2) levels. Other high-level electronic-structure methods (MR-CISD and MS-CASPT2) are involved to benchmark our dynamics results. Through the analysis of the reaction pathways from the ground state minimum to the relevant CIs, we expect that the excited-state dynamical features obtained at the MR-CISD and MS-CASPT2 levels should be very similar to those at the SA-CASSCF level. The comparison of results obtained using different excited-state electronic-structure methods could provide guidance for further studies of similar systems.

The Diels-Alder reactions of seven 1,2,4,5-tetrazines with unstrained and strained alkenes and alkynes were studied with quantum mechanical calculations (M06-2X density functional theory) and analyzed with the distortion/interaction model. The higher reactivities of alkenes compared to alkynes in the Diels-Alder reactions with tetrazines arise from the differences in both interaction and distortion energies. Alkenes have HOMO energies higher than those of alkynes and therefore stronger interaction energies in inverse-electron-demand Diels-Alder reactions with tetrazines. We have also found that the energies to distort alkenes into the Diels-Alder transition-state geometries are smaller than for alkynes in these reactions. The strained dienophiles, trans-cyclooctene and cyclooctyne, are much more reactive than unstrained trans-2-butene and 2-butyne, because they are predistorted toward the Diels-Alder transition structures. The reactivities of substituted tetrazines correlate with the electron-withdrawing abilities of the substituents. Electron-withdrawing groups lower the LUMO+1 of tetrazines, resulting in stronger interactions with the HOMO of dienophiles. Moreover, electron-withdrawing substituents destabilize the tetrazines, and this leads to smaller distortion energies in the Diels-Alder transition states.

The properties of two ladder-type semiconductors {M1: 2,2′-(2,7-dihexy1-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diylidene) dimalononitrile and M2: 2,7-dihexy1-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione} as the n-type and ambipolar organic materials are systematically investigated using the first-principle density functional theory combined with the Marcus–Hush electron transfer theory. It is found that the substitution of M1 induces large changes in its electron-transfer mobility of 1.370 cm2 V−1 s−1. M2 has both large electron- and hole-transfer mobility of 0.420 and 0.288 cm2 V−1 s−1, respectively, which indicates that M2 is potentially a high efficient ambipolar organic semiconducting material. Both the M1 and M2 crystals show remarkable anisotropic behavior. A proper design of the n-type and ambipolar organic electronic materials, which may have high mobility performance, is suggested based on the investigated two molecules.

We present theoretical investigations on structure‐property correlations in fluorenone (FLO) and benzothiadiazole (BT) substituted oligofluorenes (OFLs) derived mainly from the chain morphology, thermal vibration and conjugated extent. Both the vertical absorptions and the vibrationally‐resolved absorption and fluorescence spectra have been calculated by the combination of ab initio and time‐dependent density functional theory. By properly taking into account of the anharmonic torsion potentials in the OFLs, we have reasonably reproduced the experimentally observed spectroscopic features. Both FLO and BT on‐chain chemical defects acting as charge‐trapping sites for singlet excitations, are responsible for long wave absorption and emission species, and thus alter the blue light‐emitting properties of OFLs. As temperature decreases, the electronic spectral lineshapes of FLO‐substituted oligomers become more structured. The lineshapes of BT‐substituted oligomers are always smooth and featureless because of less low collective modes resonance. A more gentle excited potential energy surface of BT‐mixed molecules can enhance electronic delocalization and achieve bigger red shifts.

An investigation on the electronic structures and structural stability of LaN under high pressure has been conducted using first-principles calculations based on density functional theory (DFT). At elevated pressures LaN is predicted to undergo a structural phase transition from NaCl-type to CsCl-type structure. The predicted transition pressure is 65 GPa. The result of elastic constants indicates that the NaCl-type structure is mechanically a stable structure and the CsCl-type strcture is not mechanically a stable one. The calculated band structure of LaN is semimetallic.the conduction and valence bands.