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In the present study, we have investigated the performance of RIJCOSX DLPNO-CCSD(T)-F12 methods for a wide range of systems. Calculations with a high-accuracy option ["DefGrid3 RIJCOSX DLPNO-CCSD(T

Density functional theory (DFT) is currently experiencing a golden age. The past two decades witnessed remarkable advances in the general applicability of density functionals in the top rungs of Jacob’s Ladder. Nevertheless, Jacob’s Ladder may have reached its highest rung in terms of dependencies on occupied (rung four) and unoccupied orbitals (rung five). Moreover, the fifth rung is associated with a computational cost far greater than the lower rungs. Another limitation is that each rung includes dozens of different functionals, and at present, there is no clear pathway for systematic improvements within each rung of the ladder. This highlight provides an overview of the exchange–correlation (XC) hole and how it could be used in developing new density functionals. We begin with a brief overview of the current status and challenges in developing better density functionals, followed by the intimate relationship between the XC functional and hole. We present a conceptually simple and computationally economical method for calculating the XC hole and how this method could offer new directions in developing better exchange–correlation functionals.

Angewandte Chemie / International edition 62(19), e202301301 (2023). doi:10.1002/anie.202301301, Enzymes actuate catalysis through a combination of transition state stabilization and ground state destabilization, inducing enantioselectivity through chiral binding sites. Here, we present a supramolecular model system which employs these basic principles to catalyze the enantiomerization of [5]helicene. Catalysis is hereby mediated not through a network of functional groups but through $\pi-\pi$ catalysis exerted from the curved aromatic framework of a chiral perylene bisimide (PBI) cyclophane offering a binding pocket that is intricately complementary with the enantiomerization transition structure. Although transition state stabilization originates simply from dispersion and electrostatic interactions, enantiomerization kinetics are accelerated by a factor of ca. 700 at 295 K. Comparison with the meso-congener of the catalytically active cyclophane shows that upon configurational inversion in only one PBI moiety the catalytic effect is lost, highlighting the importance of precise transition structure recognition in supramolecular enzyme mimics., Published by Wiley-VCH, Weinheim

We evaluate the performance of ten common carbon force fields for the interaction energies in double and triple layered carbon onions. In particular, we consider the C20@C60, C20@C80, C20@C180, C80@C240, C60@C240 and C240@C540 double-layer carbon onions and C60@C240@C540 and C80@C240@C540 triple-layered carbon onions. We consider the following carbon force fields: Tersoff, REBO-II, AIREBO, AIREBO-M, screened versions of Tersoff and REBO-II, LCBOP-I, 2015 and 2020 versions of ReaxFF, and the machine-learning GAP force field. We show that the ReaxFF force fields give the best performance for the interaction energies of the cabon onions relative to density functional theory interaction energies obtained at the PBE0-D3/def2-TZVP level of theory. We proceed to use the ReaxFF-15 force field to explore the interaction energies in a giant ten-layered carbon onion with a C60 core and show that the interaction energy between the outer layer and the inner layers increases linearly with the number of layers in the carbon onion (with a squared correlation coefficient of R2 = 0.9996). This linear increase in the stabilization energy with each consecutive layer may have important thermodynamic consequences for describing the formation and growth of large carbon onions.

The 21-homododecahedryl cation is a unique system in terms of its complete fluxionality based on two different rearrangements. In this work, we report the quantum tunneling effects that drive the reactions at temperatures where the semi-classical kinetics are impossible. We postulate that the tunnel effect in this system can serve to create a refrigerator that may operate at arbitrarily low temperatures.

The need for sustainable and large-scale energy supply has led to significant development of renewable energy and energy storage technologies. Divalent metal ion (Mg, Ca, and Zn) batteries are promising energy storage technologies for the sustainable energy future, but the need for suitable electrode materials have limited their commercial development. This paper investigates, at the atomic scale, the adsorption and migration of Mg, Ca, and Zn on pristine and defective graphene surfaces, to bring insight into the metal storage and mobility in graphene and carbon-based anodes for divalent metal ion batteries. Such atomistic studies can help address the challenges facing the development of novel divalent metal battery technologies, and to understand the storage differences between divalent and monovalent metal-ion batteries. The adsorption of Ca on the graphene-based system is shown to be more energetically favorable than the adsorption of both Mg and Zn, with Ca showing adsorption behavior similar to the monovalent ions (Li, Na, and K). This was further investigated in terms of metal migration on the graphene surface, with much higher migration energy barriers for Ca than for Mg and Zn on the graphene systems, leading to the trapping of Ca at defect sites to a larger extent.

Gas-sensing properties of nitrogenated holey graphene (C2N), graphdiyne (GDY) and their van der Waals heterostructure (C2N…GDY) have been studied towards particular volatile organic compounds (VOCs) by means of spin-polarized, dispersion-corrected DFT calculations. We find that VOCs such as acetone, ethanol, propanal, and toluene interact weakly with the GDY monolayer; however, the bindings are significantly enhanced with the C2N monolayer and the hybrid C2N…GDY heterostructure in AB stacking. Electron localization function (ELF) analysis shows that all VOCs are van der Waals bound (physical binding) to the 2D materials, which result in significant changes of the charge density of C2N and GDY monolayers and the C2N…GDY heterostructure. These changes alter the electronic properties of C2N and GDY, and the C2N…GDY heterostructure, upon VOC adsorption, which are investigated by density-of-states plots. We further apply thermodynamic analysis to study the sensing characteristics of VOCs under varied conditions of pressure and temperature. Our findings clearly indicate that the C2N…GDY heterostructure is a promising material for sensing of certain VOCs.

Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross-linkers. These polymers have been used in a variety of applications such as energy storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of these advances, there is a need for methods to recycle and reprocess these polymers. In this study, polymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanical compression. Upon heating these molds at relatively low temperatures (≈100 °C), chemical bonding occurs at the polymer interfaces by S-S metathesis. This method of processing is distinct from previous studies on inverse vulcanization because the polymers examined in this study do not form a liquid phase when heated. Neither compression nor heating alone was sufficient to mold these polymers into new architectures, so this is a new concept in the manipulation of sulfur polymers. Additionally, high-level ab initio calculations revealed that the weakest S-S bond in organic polysulfides decreases linearly in strength from a sulfur rank of 2 to 4, but then remains constant at about 100 kJ mol-1 for higher sulfur rank. This is critical information in engineering these polymers for S-S metathesis. Guided by this insight, polymer repair, recycling, and repurposing into new composites was demonstrated.

Stable equilibrium compounds containing a planar antiaromatic cyclooctatetraene (COT) ring are promising candidates for organic electronic devices such as organic semiconductor transistors. The planarization of COT by incorporation into rigid planar π-systems, as well as by oxidation or reduction has attracted considerable attention in recent years. Using dispersion-corrected density functional theory calculations, we explore an alternative approach of planarizing COT derivatives by adsorption onto graphene. We show that strong π-π stacking interactions between graphene and COT derivatives induce a planar structure with an antiaromatic central COT ring. In addition to being reversible, this strategy provides a novel approach for planarizing COT without the need for incorporation into a rigid structure, atomic substitution, oxidation, or reduction.

Density functional theory (DFT) has been extensively benchmarked for energetic properties; however, less attention has been given to equilibrium structures and the effect of using a certain DFT geometry on subsequent energetic properties. We evaluate the performance of 52 contemporary DFT methods for obtaining the structures of 122 species in the W4-11-GEOM database. This dataset includes a total of 246 unique bonds: 117 H─X, 65 X─Y, 49 X═Y, and 15 XY bonds (where X and Y are first- and second-row atoms) and 133 key bond angles: 96 X-Y-H, 22 X-Y-Z, and 15 H-X-H angles. The reference geometries are optimized at the CCSD(T)/jul-cc-pV(n+d)Z level of theory (n = 5, 6). The performance of DFT is evaluated in conjunction with the Def2-nZVPP (n = T, Q), cc-pV(T+d)Z, and jul-cc-pV(T+d)Z basis sets. The root-mean-square deviations (RMSDs) over the bond distances of the best performing functionals from each rung of Jacob's Ladder are 0.0086 (SOGGA11), 0.0088 (τ-HCTH), 0.0059 (B3LYP), 0.0054 (TPSSh), and 0.0032 (DSD-PBEP86) A. We evaluate the effect of the choice of the DFT geometry on subsequent molecular energies calculated with W1-F12 theory. Geometries obtained with GGA and MGGA methods result in large RMSDs in the subsequent W1-F12 energies; however, six hybrid GGA functionals (B3LYP, B3P86, mPW3PBE, B3PW91, mPW1LYP, and X3LYP) result in an excellent performance with RMSDs between 0.25 and 0.30 kJ mol-1 relative to the CCSD(T)/CBS reference geometries. The B2GP-PLYP and mPW2-PLYP DHDFT methods result in near-CCSD(T) accuracy with RMSDs of 0.11 and 0.10 kJ mol-1 , respectively.

Reactions involving Criegee intermediates (CIs, R1 R2 COO) are important in atmospheric ozonolysis models. In recent years, density functional theory (DFT) and CCSD(T)-based ab initio methods are increasingly being used for modeling reaction profiles involving CIs. We obtain highly accurate CCSDT(Q)/CBS reaction energies and barrier heights for ring-closing reactions involving atmospherically important CIs (R1 /R2 = H, Me, OH, OMe, F, CN, cyclopropene, ethylene, acetaldehyde, and acrolein). We use this benchmark data to evaluate the performance of DFT, double-hybrid DFT (DHDFT), and ab initio methods for the kinetics and thermodynamics of these reactions. We find that reaction energies are more challenging for approximate theoretical procedures than barrier heights. Overall, taking both reaction energies and barrier heights into account, only one of the 58 considered DFT methods (the meta-GGA MN12-L) attains near chemical accuracy, with root-mean-square deviations (RMSDs) of 3.5 (barrier heights) and 4.7 (reaction energies) kJ mol-1 . Therefore, MN12-L is recommended for investigations where CCSD(T)-based methods are not computationally feasible. For reaction barrier heights performance does not strictly follow Jacob's Ladder, for example, DHDFT methods do not perform better than conventional DFT methods. Of the ab initio methods, the cost-effective CCSD(T)/CBS(MP2) approach gives the best performance for both reaction energies and barrier heights, with RMSDs of 1.7 and 1.4 kJ mol-1 , respectively. All the considered Gaussian-n methods show good performance with RMSDs below the threshold of chemical accuracy for both reaction energies and barrier heights, where G4(MP2) shows the best overall performance with RMSDs of 2.9 and 1.5 kJ mol-1 , respectively. © 2019 Wiley Periodicals, Inc.

Inspired by the promise of hydrogen (H2) as a clean alternate to the existing energy sources, we have employed spin-polarized density functional theory calculations on a recently designed two-dimensional C 4 N monolayer as a promising H 2 storage material. By means of first principles DFT calculations, we have comprehensively studied the geometric and electronic properties of pristine, defected and metal-doped C 4 N nanosheets and further explored their H 2 storage properties. We found that light metal dopants such as Li, Na, K, Mg, and Ca bind strongly to defects on a C 4 N nanosheet with binding energies of 3–4 eV per dopant. These binding energies are sufficiently strong to surpass metal clustering. Thermal stability of the metal-doped C 4 N nanosheets has been further verified by means of ab initio molecular dynamics simulations. The bonding nature of the metal dopants with the C 4 N nanosheet has been studied through Bader analysis and Roby-Gould methods and the electronic properties were studied through density of states. We found that each dopant in the metal-doped C 4 N nanosheet can bind up to five H 2 molecules with adsorption energies ranging between 0.15 and 0.60 eV/ H 2 , which results in optimal H 2 storage capacities. Finally, we employed thermodynamic analysis to investigate the H 2 adsorption/desorption mechanism under practical operating conditions.

Based on spin-polarized DFT calculations, we have studied the interaction mechanism of recently synthesized blue phosphorene (BlueP) monolayers towards selected key volatile organic compounds (VOCs) such as acetone, ethanol and propanal. Our binding energy analysis shows that pristine BlueP weakly binds the VOCs and that this binding does not appreciably change the electronic properties of the monolayer – a prerequisite for any sensing material. However, mono, di, and tri-vacancy defects and Si/S-substitutional doping significantly enhance the binding energies with VOCs. Density of state (DOS) calculations show that upon adsorption of VOCs, mono-vacancy and S-substituted BlueP monolayers undergo a major change in electronic structure, which make them potential candidates for VOCs sensing materials. By contrast, binding of VOCs to di- and tri-vacancy and Si-substitution sites does not alter the electronic structure of BlueP monolayers drastically, therefore, are not qualified for VOCs sensing applications.

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

Motivated by the promise of two-dimensional nanostructures in the field of gas sensing, we have employed van der Waals corrected density functional theory calculations to study the structural, electronic and gas sensing propensities of the recently designed Si2BN monolayer. Our rigorous simulations reveal that the representative members of nitrogen-containing gases (NCGs) such as NO, NO2 and NH3 binds extremely strongly on pristine Si2BN monolayer. However, a strong dissociative adsorption in case of NO and NO2 would poison the Si2BN and ultimately reversibility of the monolayer would be compromised. Exploring the sensing mechanism in more realistic pre-oxidized conditions, the binding characteristics of O2@Si2BN changed dramatically, resulting into much lower adsorption in associative manner for all NO, NO2 and NH3. A visible change in work function indicates the variation in conductivity of O2@Si2BN upon the exposure of incident gases. Sustainable values of binding energies would also ensure a quick recovery time that makes O2@Si2BN an efficient nano sensor for pollutants like NCGs.

The pursuit of a material capable of storing a high capacity of hydrogen (H2) efficiently has prompted us to study the structural, electronic and H2 storage properties of recently designed two-dimensional BN2 nanosheets. Our spin-polarized density functional theory based calculations have revealed that the pristine BN2 barely anchor H2 molecules, however, alkali metal (AM) doping enhances the binding energies drastically. Van der Waals corrected energetics analysis established a uniform distribution of AMs over the BN2 monolayers even at a high doping concentration of 12.50%, which ensure the reversibility of the systems. Bader charge analysis, Roby-Gould bond index method, and electron localization function isosurfaces conclude the transfer of charges from AMs to BN2, which has resulted into strong ionic bonds between the former and the latter. The presence of partial positive charges on each of the AMs would adsorb multiple H2 molecules with binding energies that are ideal for mobile H2 storage applications. Considerably high H2 storage capacities of 6.75%, 6.87% and 6.55% could be achieved with 3Li@BN2, 3Na@BN2 and 3K@BN2 systems, respectively that guarantees the promise of AMs decorated BN2 as a promising H2 storage material.

Nitroxide radicals have previously been successfully used as electrodes in all-organic radical batteries. However, one drawback of these batteries is significantly reduced redox potentials, in comparison to that of widely used lithium-ion batteries, making their energy-producing capacity rather small for use as a primary battery. In addition, strong propensity of nitroxide radicals to engage in side reactions with traditional electrolytes based on molecular solvents give rise to a series of undesirable and irreversible byproducts, thus significantly reducing the life of nitroxide batteries. Ionic liquids (ILs) have previously demonstrated their ability to reduce the reactivity of radicals through strong intermolecular interactions. In this study, we investigate the use of ILs as electrolytes with the view of increasing redox potentials of nitroxide radicals. A series of imidazolium, phosphonium, and pyrrolidinium-based ILs coupled with widely used anions were chosen to predict redox potentials of the 2,2,...

Polymers are an attractive anchoring platform for the synthesis of radioimmunoconjugates. They enable independent control over the amount of radioisotope loading and antibody attachment, which is pivotal in developing tailorable formulations for personalised medicine. Herein, we report the synthesis of p(HEMA-ran-GMA) for the conjugation of lutetium ions and rituximab as a functional platform for radioimmunotherapy. We demonstrate the suitability of this platform using non-Hodgkin's lymphoma cells.

Perylenequinones are a class of aromatic polyketides characterised by a highly conjugated pentacyclic core, which confers them with potent light-induced bioactivities and unique photophysical properties. Despite the biosynthetic gene clusters for the perylenequinones elsinochrome A (1), cercosporin (4) and hypocrellin A (6) being recently identified, key biosynthetic aspects remain elusive. Here, we first expressed the intact elc gene cluster encoding 1 from the wheat pathogen Parastagonospora nodorum heterologously in Aspergillus nidulans on a yeast-fungal artificial chromosome (YFAC). This led to the identification of a novel flavin-dependent monooxygenase, ElcH, responsible for oxidative enolate coupling of a perylenequinone intermediate to the hexacyclic dihydrobenzo(ghi)perylenequinone in 1. In the absence of ElcH, the perylenequione intermediate formed a hexacyclic cyclohepta(ghi)perylenequinone system via an intramolecular aldol reaction resulting in 6 and a novel hypocrellin 12 with opposite helicity to 1. Theoretical calculations supported that 6 and 12 resulted from atropisomerisation upon formation of the 7-membered ring. Using a bottom-up pathway reconstruction approach on a tripartite YFAC system developed in this study, we uncovered that both a berberine bridge enzyme-like oxidase ElcE and a laccase-like multicopper oxidase ElcG are involved in the double coupling of two naphthol intermediates to form the perylenequinone core. Gene swapping with the homologs from the biosynthetic pathway of 4 showed that cognate pairing of the two classes of oxidases is required for the formation of the perylenequinone core, suggesting the involvement of protein–protein interactions.

Herein we demonstrated that the shape and phase of colloidal ZnSe nanocrystals can be spontaneously tuned through tailoring the selenium precursor reactivity in a phosphine-free reaction system. Selenium species with diverse reaction activities, i.e. Se22− or Se2−, were produced by the addition of different volumes of reductant superhydride (lithium triethylborohydride). Theoretical calculation of ΔGr indicates that superhydride-reduced Se22− is less active than Se2− for the reaction with a Zn precursor. Nanoparticle growth using Se22− produces wurtzite ZnSe nanorods whereas the reaction of more reactive Se2− with the zinc precursor leads to the formation of spherical zinc blende ZnSe nanodots. This work not only provides a facile synthetic approach for the preparation of high quality ZnSe nanocrystals but also gives insights into the shape and phase control of other colloidal nanocrystals.

Using hydrogen as an energy carrier requires new technological solutions for its onboard storage. The exploration of two-dimensional (2D) materials for hydrogen storage technologies has been motivated by their open structures, which facilitates fast hydrogen kinetics. Herein, the hydrogen storage properties of lightweight metal functionalized r57 haeckelite sheets are studied using density functional theory (DFT) calculations. H2 molecules are adsorbed on pristine r57 via physisorption. The hydrogen storage capacity of r57 is improved by decorating it with alkali and alkaline-earth metals. In addition, the in-plane substitution of r57 carbons with boron atoms (B@r57) both prevents the clustering of metals on the surface of 2D material and increases the hydrogen storage capacity by improving the adsorption thermodynamics of hydrogen molecules. Among the studied compounds, B@r57-Li4, with its 10.0 wt% H2 content and 0.16 eV/H2 hydrogen binding energy, is a promising candidate for hydrogen storage applications. A further investigation, as based on the calculated electron localization functions, atomic charges, and electronic density of states, confirm the electrostatic nature of interactions between the H2 molecules and the protruding metal atoms on 2D haeckelite sheets. All in all, this work contributes to a better understanding of pure carbon and B-doped haeckelites for hydrogen storage.

We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic-type reaction schemes. We show that DFTB3-D/3ob can accurately predict Δf H values of the 1812 structural isomers of C60 , reproduce subtle trends in Δf H values for 24 isolated pentagon rule (IPR) isomers of C84 , and predict Δf H values of giant fullerenes that are in effectively exact agreement with benchmark DSD-PBEP86/def2-QZVPP calculations. For fullerenes up to C320 , DFTB Δf H values are within 1.0 kJ mol-1 of DSD-PBEP86/def2-QZVPP values per carbon atom, and on a per carbon atom basis DFTB3-D/3ob yields exactly the same numerical trend of (Δf H [per carbon] = 722n-0.72 + 5.2 kJ mol-1 ). DFTB3-D/3ob is therefore an accurate replacement for high-level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures.

Noncovalent interactions are an integral part of the modern catalysis toolbox. Although stronger noncovalent interactions such as hydrogen bonding are commonly the main driving force of catalysis, π-π interactions typically provide smaller additional stabilizations, for example, to afford selectivity enhancements. Here, it is shown computationally that pristine graphene flakes may efficiently catalyze the skeletal inversions of various benzannulated cyclooctatetraene derivatives, providing an example of a catalytic process driven solely by π-π stacking interactions. Hereby, the catalytic effect results from disproportionate shape complementarity between catalyst and transition structure compared with catalyst and reactant. An energy decomposition analysis reveals electrostatic and, especially with increasing system size, to a larger extent, dispersion interactions as the origin of stabilization.

Inverse vulcanization is a copolymerization of elemental sulfur and alkenes that provides unique materials with high sulfur content (typically ≥50% sulfur by mass). These polymers contain a dynamic and reactive polysulfide network that creates many opportunities for processing, assembly, and repair that are not possible with traditional plastics, rubbers and thermosets. In this study, we demonstrate that two surfaces of these sulfur polymers can be chemically joined at room temperature through a phosphine or amine-catalyzed exchange of the S–S bonds in the polymer. When the nucleophile is pyridine or triethylamine, we show that S–S metathesis only occurs at room temperature for a sulfur rank > 2—an important discovery for the design of polymers made by inverse vulcanization. This mechanistic understanding of the S–S metathesis was further supported with small molecule crossover experiments in addition to computational studies. Applications of this chemistry in latent adhesives, additive manufacturing, polymer repair, and recycling are also presented.

Polymeric carbon nitride materials have been used in numerous light‐to‐energy conversion applications ranging from photocatalysis to optoelectronics. For a new application and modelling, we first refined the crystal structure of potassium poly(heptazine imide) (K‐PHI)—a benchmark carbon nitride material in photocatalysis—by means of X‐ray powder diffraction and transmission electron microscopy. Using the crystal structure of K‐PHI, periodic DFT calculations were performed to calculate the density‐of‐states (DOS) and localize intra band states (IBS). IBS were found to be responsible for the enhanced K‐PHI absorption in the near IR region, to serve as electron traps, and to be useful in energy transfer reactions. Once excited with visible light, carbon nitrides, in addition to the direct recombination, can also undergo singlet–triplet intersystem crossing. We utilized the K‐PHI centered triplet excited states to trigger a cascade of energy transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2) as a starting point to synthesis up to 25 different N‐rich heterocycles., The triplet excited states of the new heterogeneous triplet sensitizer, potassium poly(heptazine imide),can be used to trigger a cascade of energy‐transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2), as a starting point to synthesize N‐rich heterocycles. In this way aldoximes can be converted into 1,2,4‐oxadiazoles under visible light irradiation.

Crotonaldehyde, a common environmental pollutant and product of endogenous lipid peroxidation, reacts with guanine to form DNA adducts with pronounced genotoxicity and mutagenicity. Here, we explore the molecular mechanism of this adduct formation using double-hybrid density functional theory methods. The reaction can be envisaged to occur in a two-step fashion via an aza-Michael addition leading to an intermediate ring-open adduct followed by a cyclization reaction giving the mutagenic ring-closed adduct. We find that (i) a 1,2-type addition is favored over a 1,4-type addition for the aza-Michael addition, and (ii) an initial tautomerization of the guanine moiety in the resulting ring-open adduct significantly reduces the barrier toward cyclization compared to the direct cyclization of the ring-open adduct in its keto-form. Overall, the aza-Michael addition is found to be rate-determining. We further find that participation of a catalytic water molecule significantly reduces the energy barriers of both the addition and cyclization reaction. © 2018 Wiley Periodicals, Inc.

Smart regulation of substance permeability through porous membranes is highly desirable for membrane applications. Inspired by the stomatal closure feature of plant leaves at relatively high temperature, here we report a nano-gating membrane with a negative temperature-response coefficient that is capable of tunable water gating and precise small molecule separation. The membrane is composed of poly(N-isopropylacrylamide) covalently bound to graphene oxide via free-radical polymerization. By virtue of the temperature tunable lamellar spaces of the graphene oxide nanosheets, the water permeance of the membrane could be reversibly regulated with a high gating ratio. Moreover, the space tunability endows the membrane with the capability of gradually separating multiple molecules of different sizes. This nano-gating membrane expands the scope of temperature-responsive membranes and has great potential applications in smart gating systems and molecular separation., The smart regulation of substance permeability is highly desirable for membrane separation technologies. Here, the authors design a poly(N-isopropylacrylamide)-grafted graphene oxide membrane with temperature tunable lamellar spaces, allowing for water gating and size-variable molecular separations.

Atomization reactions are among the most challenging tests for electronic structure methods. We use the first-principles Weizmann-4 (W4) computational thermochemistry protocol to generate the W4-17 dataset of 200 total atomization energies (TAEs) with 3σ confidence intervals of 1 kJ mol-1 . W4-17 is an extension of the earlier W4-11 dataset; it includes first- and second-row molecules and radicals with up to eight non-hydrogen atoms. These cover a broad spectrum of bonding situations and multireference character, and as such are an excellent benchmark for the parameterization and validation of highly accurate ab initio methods (e.g., CCSD(T) composite procedures) and double-hybrid density functional theory (DHDFT) methods. The W4-17 dataset contains two subsets (i) a non-multireference subset of 183 systems characterized by dynamical or moderate nondynamical correlation effects (denoted W4-17-nonMR) and (ii) a highly multireference subset of 17 systems (W4-17-MR). We use these databases to evaluate the performance of a wide range of CCSD(T) composite procedures (e.g., G4, G4(MP2), G4(MP2)-6X, ROG4(MP2)-6X, CBS-QB3, ROCBS-QB3, CBS-APNO, ccCA-PS3, W1, W2, W1-F12, W2-F12, W1X-1, and W2X) and DHDFT methods (e.g., B2-PLYP, B2GP-PLYP, B2K-PLYP, DSD-BLYP, DSD-PBEP86, PWPB95, ωB97X-2(LP), and ωB97X-2(TQZ)). © 2017 Wiley Periodicals, Inc.

Water contamination is generally considered to be detrimental to the performance of aprotic lithium–air batteries, whereas this view is challenged by recent contrasting observations. This has provoked a range of discussions on the role of water and its impact on batteries. In this work, a distinct battery chemistry that prevails in water-contaminated aprotic lithium–oxygen batteries is revealed. Both lithium ions and protons are found to be involved in the oxygen reduction and evolution reactions, and lithium hydroperoxide and lithium hydroxide are identified as predominant discharge products. The crystallographic and spectroscopic characteristics of lithium hydroperoxide monohydrate are scrutinized both experimentally and theoretically. Intriguingly, the reaction of lithium hydroperoxide with triiodide exhibits a faster kinetics, which enables a considerably lower overpotential during the charging process. The battery chemistry unveiled in this mechanistic study could provide important insights into the understanding of nominally aprotic lithium–oxygen batteries and help to tackle the critical issues confronted., Water is believed to undermine the performance of aprotic lithium–air batteries. However, the authors here disclose different battery chemistry, showing that both lithium ions and protons are involved in the battery reactions in the presence of water, leading to an unprecedented dynamic product.

We obtained accurate thermochemical properties for the ortho-, meta-, and para-dicarborane isomers (C2B10H12) by means of explicitly correlated high-level thermochemical procedures. The thermochemical properties include heats of formation, isomerization energies, C–H and B–H bond dissociation energies (BDEs), and ionization potentials. Of these only the ionization potentials are known experimentally. Our best theoretical ionization potentials, obtained by means of the ab initio W1–F12 thermochemical protocol, was 241.50 kcal mol–1 (para-dicarborane), 238.45 kcal mol–1 (meta-dicarborane), and 236.54 kcal mol–1 (ortho-dicarborane). These values agree with the experimental values adopted by the National Institute of Standards and Technology (NIST) thermochemical tables to within overlapping uncertainties. However, they suggest that the experimental values may represent significant underestimations. For all isomers, the C–H BDEs are systematically higher than the B–H BDEs because of the relative stability of the boron-centred radicals. The C–H BDEs for the three isomers cluster within a narrow energetic interval, namely between 110.8 kcal mol–1 (para-dicarborane) and 111.7 kcal mol–1 (meta-dicarborane). The B–H BDEs cluster within a larger interval ranging between 105.8 and 108.1 kcal mol–1 (both obtained for ortho-dicarborane). We used our benchmark W1–F12 data to assess the performance of a number of lower cost composite ab initio methods. We found that the Gaussian-3 procedures (G3(MP2)B3 and G3B3) result in excellent performance with overall root-mean-square deviations (RMSDs) of 0.3–0.4 kcal mol–1 for the isomerization, ionization, and bond dissociation energies. However, the Gaussian-4 procedures (G4, G4(MP2), and G4(MP2)-6X) showed relatively poor performance with overall RMSDs of 1.3–3.7 kcal mol–1.

The recent experimental synthesis of the two-dimensional (2D) boron-graphdiyne (BGDY) nanosheet has motivated us to investigate its structural, electronic, and energy storage properties. BGDY is a particularly attractive candidate for this purpose due to uniformly distributed pores which can bind the light-metal atoms. Our DFT calculations reveal that BGDY can accommodate multiple light-metal dopants (Li, Na, K, Ca) with significantly high binding energies. The stabilities of metal functionalized BGDY monolayers have been confirmed through ab initio molecular dynamics simulations. Furthermore, significant charge-transfer between the dopants and BGDY sheet renders the metal with a substantial positive charge, which is a prerequisite for adsorbing hydrogen (H2) molecules with appropriate binding energies. This results in exceptionally high H2 storage capacities of 14.29, 11.11, 9.10 and 8.99 wt% for the Li, Na, K and Ca dopants, respectively. These H2 storage capacities are much higher than many 2D materials such as graphene, graphane, graphdiyne, graphyne, C2N, silicene, and phosphorene. Average H2 adsorption energies for all the studied systems fall within an ideal window of 0.17–0.40 eV/H2. We have also performed thermodynamic analysis to study the adsorption/desorption behavior of H2, which confirms that desorption of the H2 molecules occurs at practical conditions of pressure and temperature.

We employ first-principles calculations based on density functional theory (DFT) to investigate the adsorption characteristics of a novel 2D material, hexagonal yttrium nitride (h-YN) monolayer, towards sulfur-containing gases (SCG) such as H2S and SO2. Dispersion corrected DFT calculations were carried out to explore the adsorption mechanism, structural and electronic properties of pristine and SCG-adsorbed h-YN (with and without the presence of O2). Our calculations reveal that both H2S and SO2 are strongly adsorbed on pristine h-YN with adsorption energies of –3.24 and –4.21 eV, respectively. However, the presence of molecular oxygen plays an important role in reducing the adsorption energies to –2.46 and –1.75 eV for H2S and SO2, respectively. Strong chemisorption, even in the presence of O2, makes h-YN suitable for non-reversible capturing of H2S and SO2. In case of SO2, molecular adsorption coupled with significant variations in the electronic properties and charge transfer indicates the suitability of h-YN for SO2 capture and a disposable sensing material.

Divalent ion batteries are potential substitutes to existing rechargeable batteries because of the high-energy density, safety, and low cost. However, the applications of divalent batteries are strongly dependent on the availability of efficient electrode materials. We herein report the adsorption and migration mechanism of divalent ions like Mg+2 and Ca+2, on two-dimensional carbon nitride monolayer (C4N). The adsorption of both Mg and Ca ions are much stronegr on C4N saturated with functional groups like hydrogen (-H), hydroxyl (-OH), and carboxylic (-COOH) as compared to the pristine monolayers, which implies the improvement in metal storage caused by the functional groups. On functionalized C4N, the first Mg binds within the binding energy range of 1.5-2.2 eV having migration barrier, at the saturated sites, of around 0.5 eV, which indicates desirable binding and robust diffuse. However, the functional groups tend to act as the trapping sites for Ca ions and the diffusion might get hindered as compared to Mg ions. In addition to binding and diffusion mechanism, charge transfer, electronic structures and open circuit volatges have also been calculated for both Mg and Ca on pristine and functionalized C4N monolayers. We find that -H, -OH, and -COOH play important role for the cyclic performance of C4N as the prospective anode material for divalent ion batteries.

Although 18-crown-6 is renowned for its binding affinity to various metal and ammonium cations, the nature and strength of its binding with neutral guest molecules is relatively unexplored. Here we report a computational study of the host : guest geometries, interaction energies and Gibbs free energies of formation of 18-crown-6 with 49 neutral guest molecules in the gas phase, using the G4(MP2) composite method. Optimized geometries are in excellent agreement with those observed in crystals, with differences readily attributed to guest : guest interactions in the solid state. Host : guest interaction energies range from −13 to −103 kJ mol−1, and the estimated Gibbs free energies of binding at 298 K correlate with the observation (or not) of the complexes in crystals. The electrostatic, dispersion, polarization and repulsion components of the interaction energy have also been estimated using the recently described CE-B3LYP model energies, providing insight into the binding nature between 18C6 and neutral molecules.

The question of whether intermolecular interactions in crystals originate from localized atom center dot center dot center dot atom interactions or as a result of holistic molecule center dot center dot center dot molecule close packing is a matter of continuing debate. In this context, the newly introduced Roby-Gould bond indices are reported for intermolecular 'sigma-hole' interactions, such as halogen bonding and chalcogen bonding, and compared with those for hydrogen bonds. A series of 97 crystal systems exhibiting these interaction motifs obtained from the Cambridge Structural Database (CSD) has been analysed. In contrast with conventional bond-order estimations, the new method separately estimates the ionic and covalent bond indices for atom center dot center dot center dot atom and molecule center dot center dot center dot molecule bond orders, which shed light on the nature of these interactions. A consistent trend in charge transfer from halogen/chalcogen bond-acceptor to bond-donor groups has been found in these intermolecular interaction regions via Hirshfeld atomic partitioning of the electron populations. These results, along with the 'conservation of bond orders' tested in the interaction regions, establish the significant role of localized atom center dot center dot center dot atom interactions in the formation of these intermolecular binding motifs.

Covalency and ionicity are orthogonal rather than antipodal concepts. We demonstrate for the case of siloxane systems [R3Si-(O-SiR2)(n)-O-SiR3] that both covalency and ionicity of the Si-O bonds impact on the basicity of the Si-O-Si linkage. The relationship between the siloxane basicity and the Si-O bond character has been under debate since previous studies have presented conflicting explanations. It has been shown with natural bond orbital methods that increased hyperconjugative interactions of LP(O)->sigma*(Si-R) type, that is, increased orbital overlap and hence covalency, are responsible for the low siloxane basicity at large Si-O-Si angles. On the other hand, increased ionicity towards larger Si-O-Si angles has been revealed with real-space bonding indicators. To resolve this ostensible contradiction, we perform a complementary bonding analysis, which combines orbital-space, real-space, and bond-index considerations. We analyze the isolated disiloxane molecule H3SiOSiH3 with varying Si-O-Si angles, and n-membered cyclic siloxane systems Si2H4O(CH2)(n-3). All methods from quite different realms show that both covalent and ionic interactions increase simultaneously towards larger Si-O-Si angles. In addition, we present highly accurate absolute hydrogen-bond interaction energies of the investigated siloxane molecules with water and silanol as donors. It is found that intermolecular hydrogen bonding is significant at small Si-O-Si angles and weakens as the Si-O-Si angle increases until no stable hydrogen-bond complexes are obtained beyond phi(SiOSi) = 168 degrees, angles typically displayed by minerals or polymers. The maximum hydrogen-bond interaction energy, which is obtained at an angle of 105 degrees, is 11.05 kJ mol(-1) for the siloxane-water complex and 18.40 kJ mol(-1) for the siloxane-silanol complex.

The S66 benchmark for noncovalent interactions has been re-evaluated using explicitly correlated methods with basis sets near the one-particle basis set limit. It is found that post-MP2 "high-level corrections" are treated adequately well using a combination of CCSD(F12*) with (aug-)cc-pVTZ-F12 basis sets on the one hand, and (T) extrapolated from conventional CCSD(T)/heavy-aug-cc-pV{D,T}Z on the other hand. Implications for earlier benchmarks on the larger S66x8 problem set in particular, and for accurate calculations on noncovalent interactions in general, are discussed. At a slight cost in accuracy, (T) can be considerably accelerated by using sano-V{D,T}Z+ basis sets, while half-counterpoise CCSD(F12*)(T)/cc-pVDZ-F12 offers the best compromise between accuracy and computational cost., Comment: Australian Journal of Chemistry, in press [Graham S. Chandler special issue]

Hydrocarbon cages are key reference materials for the validation and parameterization of computationally cost-effective procedures such as density functional theory (DFT), semiempirical molecular orbital theory, and molecular mechanics. We obtain accurate total atomization energies (TAEs) and heats of formation (ΔfH°298) for platonic and prismatic hydrocarbon cages by means of the Wn-F12 explicitly correlated thermochemical protocols. We consider the following kinetically stable (CH)n polycyclic hydrocarbon cages: (i) platonic hydrocarbons (tetrahedrane, cubane, and dodecahedrane), (ii) prismatic hydrocarbons (triprismane, cubane, and pentaprismane), and (iii) one truncated tetrahedrane (octahedrane). Our best theoretical heat of formation for cubane (144.8 kcal mol−1) suggests that the experimental value adopted by the NIST thermochemical database (142.7 ± 1.2 kcal mol−1) should be revised upwards by ∼2 kcal mol−1. Our best heat of formation for dodecahedrane (20.2 kcal mol−1) suggests that the semiexperimental value (22.4 ± 1 kcal mol−1) should be revised downward by ∼2 kcal mol−1. We use our benchmark Wn-F12 TAEs to evaluate the performance of a variety of computationally less demanding composite thermochemical procedures. These include the Gaussian-n (Gn) and the complete basis set (CBS) methods. The CBS-QB3 and CBS-APNO procedures show relatively poor performance with root-mean-squared deviations (RMSDs) of 4.2 and 2.5 kcal mol−1, respectively. The best performers of the Gn procedures are G4 and G3(MP2)B3 (RMSD = 0.5 and 0.6 kcal mol−1, respectively), while the worst performers are G3 and G4(MP2)-6X (RMSD = 2.1 and 2.9 kcal mol−1, respectively). Isodesmic and even homodesmotic reactions involving these species are surprisingly challenging targets for DFT computations. © 2015 Wiley Periodicals, Inc.

We obtained accurate gas-phase tautomerization energies for a set of 14 guanine tautomers by means of high-level thermochemical procedures approximating the CCSD(T) energy at the complete basis set (CBS) limit. For the five low-lying tautomers, we use the computationally demanding W1-F12 composite method for obtaining the tautomerization energies. The relative W1-F12 tautomerization enthalpies at 298 K are: 0.00 (1), 2.37 (2), 2.63 (3), 4.03 (3′), and 14.31 (4) kJ mol−1. Thus, as many as four tautomers are found within a small energy window of less than 1.0 kcal mol−1 (1 kcal mol−1 = 4.184 kJ mol−1). We use these highly accurate W1-F12 tautomerization energies to evaluate the performance of a wide range of lower-level composite ab initio procedures. The Gn composite procedures (G4, G4(MP2), G4(MP2)-6X, G3, G3B3, G3(MP2), and G3(MP2)B3) predict that the enol tautomer (3) is more stable than the keto tautomer (2) by amounts ranging from 0.36 (G4) to 1.28 (G3(MP2)) kJ mol−1. We also find that an approximated CCSD(T)/CBS energy calculated as HF/jul-cc-pV{D,T}Z + CCSD/jul-cc-pVTZ + (T)/jul-cc-pVDZ results in a root-mean-square deviation (RMSD) of merely 0.11 kJ mol−1 relative to the W1-F12 reference values. We use this approximated CCSD(T)/CBS method to obtain the tautomerization energies of 14 guanine tautomers. The relative tautomerization enthalpies at 298 K are: 0.00 (1), 2.20 (2), 2.51 (3), 4.06 (3′), 14.30 (4), 25.65 (5), 43.78 (4′), 53.50 (6′), 61.58 (6), 77.37 (7), 82.52 (8′), 86.02 (9), 100.70 (10), and 121.01 (8) kJ mol−1. Using these tautomerization enthalpies, we evaluate the performance of standard and composite methods for the entire set of 14 guanine tautomers. The best-performing procedures emerge as (RMSDs are given in parentheses): G4(MP2)-6X (0.51), CCSD(T)+ΔMP2/CBS (0.52), and G4(MP2) (0.64 kJ mol−1). The worst performers are CCSD(T)/AVDZ (1.05), CBS-QB3 (1.24), and CBS-APNO (1.38 kJ mol−1).

To nurture the full potential of hydrogen (H2) as a clean energy carrier, its efficient storage under ambient conditions is of great importance. Owing to the potential of material-based H2 storage as a promising option, we have employed here first principles density functional theory calculations to study the H2 storage properties of recently synthesized C3N monolayers. Despite possessing fascinating structural and mechanical properties C3N monolayers weakly bind H2 molecules. However, our van der Waals corrected simulations revealed that the binding properties of H2 on C3N could be enhanced considerably by suitable Sc and Ti doping. The stabilities of Sc and Ti dopants on a C3N surface has been verified by means of reaction barrier calculations and ab initio molecular dynamics simulations. Upon doping with C3N, the existence of partial positive charges on both Sc and Ti causes multiple H2 molecules to bind to the dopants through electrostatic interactions with adsorption energies that are within an ideal range. A drastically high H2 storage capacity of 9.0 wt% could be achieved with two-sided Sc/Ti doping that ensures the promise of C3N as a high-capacity H2 storage material.

Density functional theory (DFT) is the only quantum-chemical avenue for calculating thermochemical/kinetic properties of large polycyclic aromatic hydrocarbons (PAHs) such as graphene nanoflakes. Using CCSD(T)/CBS PAH isomerization energies, we find that all generalized gradient approximation (GGA) and meta GGA DFT functionals have severe difficulties in describing isomerization energies in PAHs. The poor performance of these functionals is demonstrated by the following root-mean-square deviations (RMSDs) obtained for a database of C14 H10 and C18 H12 isomerization energies. The RMSDs for the GGAs range between 6.0 (BP86-D3) and 23.0 (SOGGA11) and for the meta GGAs they range between 3.5 (MN12-L) and 11.9 (τ-HCTH) kJ mol-1 . These functionals (including the dispersion-corrected methods) systematically and significantly underestimate the isomerization energies. A consequence of this behavior is that they all predict that chrysene (rather than triphenylene) is the most stable C18 H12 isomer. A general improvement in performance is observed along the rungs of Jacob's Ladder; however, only a handful of functionals from rung four give good performance for PAH isomerization energies. These include functionals with high percentages (40-50%) of exact Hartree-Fock exchange such as the hybrid GGA SOGGA11-X (RMSD = 1.7 kJ mol-1 ) and the hybrid-meta GGA BMK (RMSD = 1.3 kJ mol-1 ). Alternatively, the inclusion of lower percentages (20-30%) of exact exchange in conjunction with an empirical dispersion correction results in good performance. For example, the hybrid GGA PBE0-D3 attains an RMSD of 1.5 kJ mol-1 , and the hybrid-meta GGAs PW6B95-D3 and B1B95-D3 result in RMSDs below 1 kJ mol-1 . © 2016 Wiley Periodicals, Inc.

Proficient capture of carbon dioxide (CO2) is considered to be a backbone for environment protection through countering the climate change caused by mounting carbon content. Here we present a comprehensive mechanism to design novel functional nanostructures capable of capturing a large amount of CO2 efficiently. By means of van der Waals corrected density functional theory calculations, we have studied the structural, electronic and CO2 storage properties of carbon nitride (g-C6N8) nano sheets functionalized with a range of transition metal (TM) dopants ranging from Sc to Zn. The considered TMs bind strongly to the nano sheets with binding energies exceeding their respective cohesive energies, thus abolishing the possibility of metal cluster formation. Uniformly dispersed TMs change the electronic properties of semiconducting g-C6N8 through the transfer of valence charges from the former to the latter. This leaves all the TM dopants with significant positive charges, which are beneficial for CO2 adsorption. We have found that each TM's dopants anchor a maximum of four CO2 molecules with suitable adsorption energies (-0.15 to -1.0 eV) for ambient condition applications. Thus g-C6N8 nano sheets functionalized with selected TMs could serve as an ideal sorbent for CO2 capture.

Radical stabilization energies (RSE)s have been calculated for a variety of boryl radicals complexed to Lewis bases at the G3(MP2)-RAD level of theory. These are referenced to the B-H bond dissociation energy (BDE) in BH(3) determined at W4.3 level. High RSE values (and thus low BDE(B-H) values) have been found for borane complexes of a variety of five- and six-membered ring heterocycles. Variations of RSE values have been correlated with the strength of Lewis acid-Lewis base complex formation at the boryl radical stage. The analysis of charge- and spin-density distributions shows that spin delocalization in the boryl radical complexes constitutes one of the mechanisms of radical stabilization.

Ingenol esters have been identified as potent anticancer and HIV latency reversing agents. Ingenol-3-angelate was recently approved as a topical treatment for precancerous actinic keratosis skin lesions. It was found, however, that ingenol esters can undergo a series of acyl rearrangements, which may affect their biological potency and the shelf-life of drug formulations. We use double-hybrid density functional theory to explore the mechanisms for the uncatalysed and water-catalysed acyl migrations in a model ingenol ester. The uncatalysed reaction may proceed either via a concerted mechanism or via a stepwise mechanism that involves a chiral orthoester intermediate. We find that the stepwise pathway is kinetically preferred by a significant amount of ΔΔH‡298 = 44.5 kJ mol−1. The uncatalysed 3-O-acyl to 5-O-acyl and 5-O-acyl to 20-O-acyl stepwise rearrangements involve cyclisation and ring-opening steps, both concomitant with a proton transfer. We find that the ring-opening step is the rate-determining step for both rearrangements, with reaction barrier heights of ΔH‡298 = 251.6 and 177.1 kJ mol−1 respectively. The proton transfers in the cyclisation and ring-opening steps may be catalysed by a water molecule. The water catalyst reduces the reaction barrier heights of these steps by over 90 kJ mol−1.

The potential energy surface (PES) of the ground state of the beryllium dimer poses a significant challenge for high-level ab initio electronic structure methods. Here, we present a systematic study of basis set effects over the entire PES of Be2 calculated at the full configuration interaction (FCI) level. The reference PES is calculated at the valence FCI/cc-pV{5,6}Z level of theory. We find that the FCI/cc-pV{T,Q}Z basis set extrapolation reproduces the shape of the FCI/cc-pV{5,6}Z PES as well as the binding energy and vibrational transition frequencies to within ~10 cm−1. We also use the FCI/cc-pV{5,6}Z PES to evaluate the performance of truncated coupled cluster methods (CCSD, CCSD(T), CCSDT, and CCSDT(Q)) and contemporary density functional theory methods (DFT) methods for the entire PES of Be2. Of the truncated coupled cluster methods, CCSDT(Q)/cc-pV{5,6}Z provides a good representation of the FCI/cc-pV{5,6}Z PES. The GGA functionals, as well as the HGGA and HMGGA functionals with low percentages of exact exchange tend to severely overbind the Be2 dimer, whereas BH&HLYP and M06-HF tend to underbind it. Range-separated DFT functionals tend to underbind the dimer. Double-hybrid DFT functionals show surprisingly good performance, with DSD-PBEP86 being the best performer. Møller–Plesset perturbation theory converges smoothly up to fourth order; however, fifth-order corrections have practically no effect on the PES.