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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.

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.

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.

The equilibrium geometry of the singlet ground electronic state of the bent isomer of C5H2, bent-pentadiynylidene (4; X ∼ 1 A 1 ; C 2 v ), has been theoretically investigated by means of the highly accurate W3-F12 thermochemical protocol. Five isomers of C5H2, namely linear-pentadiynylidene (1; X ∼ 3 Σ g - ; D ∞ h ), ethynylcyclopropenylidene (2; X ∼ 1 A ′ ; C s ), pentatetraenylidene (3; X ∼ 1 A 1 ; C 2 v ), ethynylpropadienylidene (5; X ∼ 1 A ′ ; C s ), and 3-(didehydrovinylidene)cyclopropene (6; X ∼ 1 A 1 ; C 2 v ) had already been identified in the laboratory. With respect to 1, the relative energy difference calculated at the CCSDT(Q)/CBS level of theory including zero-point vibrational energy corrections are: 0.66 (2), 13.53 (3), 14.12 (4), 15.40 (5), and 20.01 (6) kcal mol−1, respectively. Isomers 2–6 are associated with a non-zero dipole moment ( μ ≠ 0 ), however, except 4, all the other four isomers were identified by Fourier Transform Microwave spectroscopy, including 5 and 6 which lie higher in energy. Isomer 4 remains elusive to date. We believe that the theoretical data such as, optimal geometry, dipole moment, rotational and centrifugal distortion constants, harmonic vibrational frequencies, infra-red intensities, and isotopic shifts (12C–13C) in harmonic vibrational frequencies presented here would assist experimentalists in the identification of this elusive molecule (4).

The potent antioxidant α-tocopherol is known to trap two hydroxyl radicals leading to the formation of the experimentally observed α-tocopherylquinone product. Based on double-hybrid density functional theory calculations, we propose for the first time, a reaction mechanism for the conversion of α-tocopherol to α-tocopherylquinone. We find that a water-catalysed ring-opening reaction plays a key role in this conversion. The water catalysts act as proton shuttles facilitating the proton transfers and reducing the ring strain in the cyclic transition structures. On the basis of the proposed reaction mechanism, we proceed to design an antioxidant with potentially enhanced antioxidant properties.

The D5h → D10h isomerization in the C10 carbon cluster is investigated at the relativistic, all-electron CCSDT(Q)/CBS level. Previous high-level studies examined this isomerization at the valence CCSD(T)/CBS level. We show that capturing this isomerization energy requires accurate treatment of the CCSD(T)/CBS, post-CCSD(T), core-valence, scalar relativistic, diagonal Born–Oppenheimer, and zero-point vibrational energy components. Combining these components shows that the two structures are practically isoenergetic at 0 K (i.e., the D5h structure is more stable by merely +0.100 kcal mol−1). We also show that computationally economical composite protocols erroneously predict that the D10h structure is energetically more stable at 0 K.

Simultaneous loading of hydrophobic and hydrophilic drugs into a drug delivery system is a difficult task and challenges still remain due to opposite nature of drugs. So far, most of the drug delivery systems have been designed based on liposomes, dual emulsions or porous nano-silica cavities. The application of Graphene and its oxidized derivatives as nanocarriers (NCs) have grown rapidly in the past few years. The first part of this study, using molecular modeling methods, provides details on the possibility and the mechanism of simultaneous loading of two hydrophobic and hydrophilic drugs, Rifampicin and Isoniazid, into graphene oxide (GO). The results confirmed the possibility of simultaneous loading of drugs in GO. The binding energies, calculated at the B3LYP-D3/6-31G(d) level of theory, are: −46.5 and −14.0 kJ mol−1 for Isoniazid and Rifampicin, respectively. Drugs loading, as also evidenced in the second part of study experimentally. The drug-loaded NCs were coated with biopolymers of Chitosan and Gum Tragacanth. SEM results confirmed that GO-NCs have produced with a diameter

A single crystal Dy3Al2(AlO4)3 rare-earth nanogarnets were grown via a sol-gel combustion method using single fuel. The structure and purity of nanogarnets was confirmed by XRD analysis. The average crystallite sizes and the effective particle sizes were calculated by Scherrer and Hall-Williamson equations. The FTIR results clearly confirmed the formation of metal-oxygen and metal-metal bonds of the product. The morphological studies were affirmed the nanoscale formation of Dy3Al5O12 with approximately narrow distribution of the particles. The direct band gap energy of the nanogarnets was calculated using Tauc equation about 3.33 eV. To complement the experimental data, the structural and electronic properties were calculated using periodic density functional theory. The use of the Hubbard U parameter was used and improved the band gap to experimental values. Experimental and computational observations have rendered the Dy3Al5O12 nanogarnets can be suitable for hydrogen energy sorption. The electrochemical hydrogen storage capacity of Dy3Al5O12 was measured at about 3137 mAh/g after 15 cycles.

We evaluate the performance of carbon force fields for 1811 C60 PW6B95-D3/Def2-QZVP isomerization energies. Several force fields (most notably the machine-learning GAP-20 potential) exhibit a high statistical correlation with the DFT isomerization energies. Therefore, linear scaling of the isomerization energies can significantly improve the accuracy. The best scaled force fields attain mean-absolute deviations of 8.5 (GAP-20), 12.3 (LCBOP-I and REBO-II), and 13.3 (ABOP) kcal mol−1, which translate to mean-absolute relative deviations of 4.7% (GAP-20), 6.5% (LCBOP-I), 6.6% (REBO-II) and 7.1% (ABOP). Therefore, these force fields offer a computationally economical way for exploring the relative energies of fullerenes.

We calculate the CCSD(T)/CBS complexation energies of C6X6⋯C2Xn complexes (X = F, Cl; n = 2, 4) by means of the W1-F12 and CCSD(T)/MP2(CBS) procedures. These complexes involve π–π stacking, charge-transfer, and van der Waals interactions and their complexation energies range between 11.1 (C6F6⋯C2F2) and 34.0 (C6Cl6⋯C2Cl4) kJ mol−1. We use our best CCSD(T)/CBS data to assess the performance of DFT, double-hybrid DFT (DHDFT), and standard/composite ab initio methods. The G4 and G4(MP2) composite methods show relatively poor performance with root-mean-square deviations (RMSDs) of 8.7 and 6.3 kJ mol−1, respectively. With the main exception of the Minnesota functionals, DFT functionals without a dispersion correction do not predict binding in these complexes. Most of the conventional DFT procedures attain RMSDs above the ‘chemical accuracy’ threshold. The best performing functionals with RMSDs ≤2.0 kJ mol−1 are: B3LYP-D3, PW6B95-D3, LC-ωPBE-D3, PWPB95-D3, B2GP-PLYP-D3, and B2-PLYP-D3.

We examine the reaction of ethanol with glyoxal to form hemiacetal by means of the high-level G4(MP2) procedure. In this reaction, an intermolecular proton transfer is coupled with the formation of a covalent C O bond between the two molecules. We find a novel catalytic reaction mechanism in which an H 2 SO 4 catalyst reduces the barrier height from ∆ H ‡ 298 = 140.2 to 16.3 kJ mol −1 . It is well established that H 2 SO 4 can effectively catalyse intramolecular proton transfers. This letter shows that H 2 SO 4 can catalyse an intermolecular proton transfer that is coupled with a covalent bond formation.

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.

We evaluate the performance of standard and modified MP n procedures for a wide set of thermochemical and kinetic properties, including atomization energies, structural isomerization energies, conformational energies, and reaction barrier heights. The reference data are obtained at the CCSD(T)/CBS level by means of the W n thermochemical protocols. We find that none of the MP n -based procedures show acceptable performance for the challenging W4-11 and BH76 databases. For the other thermochemical/kinetic databases, the MP2.5 and MP3.5 procedures provide the most attractive accuracy-to-computational cost ratios. The MP2.5 procedure results in a weighted-total-root-mean-square deviation (WTRMSD) of 3.4 kJ/mol, whilst the computationally more expensive MP3.5 procedure results in a WTRMSD of 1.9 kJ/mol (the same WTRMSD obtained for the CCSD(T) method in conjunction with a triple-zeta basis set). We also assess the performance of the computationally economical CCSD(T)/CBS(MP2) method, which provides the best overall performance for all the considered databases, including W4-11 and BH76.

The CCSD(T) method is often considered as the gold standard in quantum chemistry for single-reference systems. Using W4 and W4lite theories, we calculate post-CCSD(T) contributions to the total atomization energies (TAEs) of n -alkanes and show that they reach up to 0.65 kcal/mol for n -hexane. Furthermore, we find that post-CCSD(T) contributions increase linearly with the size of the n -alkane, indicating that they will reach ∼1 kcal/mol for n -decane (C 10 H 22 ) and ∼2 kcal/mol for n -icosane (C 20 H 42 ). These results are significant since today CCSD(T)/CBS-type methods are being applied to hydrocarbons of increasing size and are assumed to give TAEs with chemical accuracy for these systems.

High-level heats of formation for C 60 are obtained through the use of reactions in which C 60 is broken down into its fundamental bowl-shaped aromatic fragments (corannulene and sumanene). The reaction enthalpies are obtained by means of the high-level G4(MP2) thermochemical protocol and reliable experimental (from the Active Thermochemical Tables, ATcT) or theoretical (from W1h theory) heats of formation are used for the molecules involved in these reactions. Our best theoretical estimate, Δ f H ° 298 [C 60 ( g )] = 2511.7 kJ mol −1 , suggests that the experimental value adopted by the NIST thermochemical database (Δ f H ° 298 [C 60 ( g )] = 2560 ± 100 kJ mol −1 ) should be revised downwards.

Benchmark reaction barrier heights for the degenerate Cope rearrangements in the highly fluxional bullvalene and semibullvalene hydrocarbon cages are obtained at the CCSDT(Q) level close to the one-particle basis set limit and include inner-shell, scalar-relativistic, and Born–Oppenheimer corrections. Our best theoretical CCSDT(Q) Gibbs free reaction barrier height for semibullvalene (ΔG298‡ = 27.9 kJ mol−1) is in good agreement with the most recent experimental value of 25.9 kJ mol−1. However, our CCSDT(Q) reaction barrier height for bullvalene (ΔG298‡ = 62.2 kJ mol−1) indicates that the most recent gas-phase experimental value of 54.8 ± 0.8 should be revised upward.

We use Gaussian-4 theory to investigate the reaction mechanism for the conversion of a 2-methylstyrene-based Criegee intermediate into o-toluic acid and 2-methylphenylformate. o-Toluic acid can be formed via an α-hydroxyalkyl-hydroperoxide intermediate with an activation energy of ΔG‡298 = 82.9 kJ mol−1 for the rate-determining-step (RDS). The RDS for the formation of 2-methylphenylformate has an activation energy of ΔG‡298 = 61.9 kJ mol−1. Formation of the o-toluic acid product is more exergonic by 67.4 kJ mol−1. Consistent with recent experimental results, our high-level calculations show that o-toluic acid is the thermodynamic product and 2-methylphenylformate is the kinetic product.

We introduce a database of 14 accurate bond dissociation energies (BDEs) of noble gas compounds. Reference CCSD(T)/CBS BDEs are obtained by means of W1 theory. We evaluate the performance of contemporary density functional theory (DFT), double-hybrid DFT (DHDFT), and composite ab initio procedures. A general improvement in performance is observed along the rungs of Jacob’s Ladder; however, only a handful of functionals give good performance for predicting the bond dissociation energies in the NGC14 database. Thus, this database represents a challenging test for DFT methods. Most of the conventional DFT functionals (71%) result in root-mean-square deviations (RMSDs) between 10.0 and 82.1 kJ mol−1. The rest of the DFT functionals attain RMSDs between 2.5 and 8.9 kJ mol−1. The best performing functionals from each rung of Jacob’s Ladder are (RMSD given in parenthesis): HCTH407 (30.9); M06-L (5.4); PBE0 (2.8); B1B95, M06, and PW6B95 (2.7–2.9); CAM-B3LYP-D3 (5.4); and B2T-PLYP (2.5 kJ mol−1).

We examine the basis-set convergence of post-CCSD(T) contributions to the dissociation energy of the highly multireference C2(1 Σ g + ) molecule. At the infinite basis set limit we obtain: CCSDT–CCSD(T)/cc-pV{6,7}Z = −2.268, CCSDT(Q)–CCSDT/cc-pV{6,7}Z = 3.420, CCSDTQ–CCSDT(Q)/cc-pV{5,6}Z = −1.151, CCSDTQ(5)–CCSDTQ/cc-pV{Q,5}Z = 0.412, CCSDTQ5–CCSDTQ(5)/cc-pV{T,Q}Z = −0.053, CCSDTQ5(6)–CCSDTQ5/cc-pV{D,T}Z = 0.060, CCSDTQ56–CCSDTQ5(6)/cc-pVTZ(1d) = 0.003, CCSDTQ56(7)–CCSDTQ56/cc-pVTZ(1d) = 0.002, and CCSDTQ567–CCSDTQ56(7)/cc-pVTZ(1d) = 0.001 kcal/mol. These post-CCSD(T) contributions add to 0.427 kcal/mol. Including the CCSD(T)/CBS energy, inner-shell, scalar relativistic, spin-orbit, DBOC, and ZPVE corrections from W4.3 theory results in a CCSDTQ567/CBS D0 value of 144.08 kcal/mol, which agrees to within overlapping uncertainties with the experimental ATcT value of 144.006 ± 0.06 kcal/mol.

We introduce a database of 20 accurate cycloreversion barrier heights of 5-membered heterocyclic rings (to be known as the CRBH20 database). In these reactions, dioxazole and oxathiazole rings are fragmented to form isocyanates, isothiocyanates, and carbonyls. The reference reaction barrier heights are obtained by means of the high-level, ab initio W1-F12 and W1w thermochemical protocols. We evaluate the performance of 65 contemporary density functional theory (DFT) and double-hybrid DFT (DHDFT) procedures. The CRBH20 database represents an extremely challenging test for these methods. Most of the conventional DFT functionals (74%) result in root-mean-square deviations (RMSDs) between 10 and 81 kJ mol −1 . The rest of the DFT functionals attain RMSDs = 5 − 10 kJ mol −1 . Of the 12 tested DHDFT functionals, only five result in RMSDs −1 . The CRBH20 dataset also proves to be a surprisingly challenging target for composite and standard ab initio procedures.

Using accurate quantum chemical calculations, we show that extended planar polycyclic aromatic hydrocarbons (PAHs) can efficiently catalyze a range of chemical processes involving non-planar aromatic systems. These include (i) bowl-to-bowl inversion of curved PAHs (e.g. corannulene and sumanene), (ii) ‘flip-flop’ inversion of helicenes (e.g. benzo[c]phenanthrene), and (iii) rotation about the Ph Ph bond in biphenyls. Non-covalent π–π interactions between the planar catalyst and the substrate stabilize the planar transition structures to a greater extent than they stabilize the non-planar reactants. These result in surprisingly large catalytic enhancements (namely, the reaction barrier heights are reduced by 21–63% of the uncatalyzed reaction barriers).

We introduce a representative database of 60 accurate diene isomerization energies obtained by means of the high-level, ab initio W n –F12 thermochemical protocols. The isomerization reactions involve a migration of one double bond that breaks the π-conjugated system. The considered dienes involve a range of hydrocarbon functional groups, including linear, branched, and cyclic moieties. This set of benchmark isomerization energies allows an assessment of the performance of more approximate theoretical procedures for the calculation of π-conjugation stabilization energies in dienes. We evaluate the performance of a large number of density functional theory (DFT) and double-hybrid DFT (DHDFT) procedures. We find that, with few exceptions (most notably BMK-D3 and M05-2X), conventional DFT procedures have difficulty describing reactions of the type: conjugated diene → non-conjugated diene, with root mean square deviations (RMSDs) between 4.5 and 11.7 kJ mol −1 . However, DHDFT procedures show excellent performance with RMSDs well below the ‘chemical accuracy’ threshold.

International audience; We investigated the formation of the naphthalene cation from the successive addition of two acetylenes on the benzene cation. A DFT approach was used for that purpose. The entry channel corresponding to the addition of the acetylenes is the energetically highest part of the entire reaction pathway. It was recalculated using the ab initio W1-F12 and G4 thermochemical protocols. At these levels, the energetically highest point in the entry channel is shown to be just below the energy of the free reactants. This Letter shows that the formation of the naphthalene cation from benzene and acetylenes should proceed in space.

The vinyl alcohol–acetaldehyde tautomerization reaction has recently received considerable attention as a potential route for the formation of organic acids in the troposphere (Andrews et al., 2012 [7]). We examine the catalytic effect of inorganic acids in the troposphere (e.g. HNO3, H2SO4 and HClO4) on the vinyl alcohol–acetaldehyde tautomerization reaction, by means high-level thermochemical procedures. We show that H2SO4 and HClO4 catalysts lead to near-zero reaction barrier heights for the vinyl alcohol → acetaldehyde reaction, and to low reaction barrier heights in the reverse direction ( Δ H 298 ‡ = 40.6 and 39.5 kJ mol - 1 , respectively).

High level ab initio calculations were undertaken on the CH$_2$OO anion and neutral species to predict the electron affinity and anion photoelectron spectrum. The electron affinity of CH$_2$OO, 0.567 eV, and barrier height for dissociation of CH$_2$OO$^-$ to O$^-$ and CH$_2$O, 16.5 kJ mol$^{-1}$, are obtained by means of the W3-F12 thermochemical protocol. Two major geometric differences between the anion and neutral, being the dihedral angle of the terminal hydrogen atoms with respect to C-O-O plane, and the O-O bond length, are reflected in the predicted spectrum as pronounced vibrational progressions.

We show that the purely first-principles Weizmann-4 (W4) computational thermochemistry method developed in our group can reproduce available Active Thermochemical Tables atomization energies for 35 molecules with a 3σ uncertainty of under 1 kJ/mol. We then employ this method to generate the W4-11 dataset of 140 total atomization energies of small first-and second-row molecules and radicals. These cover a broad spectrum of bonding situations and multireference character, and as such are an excellent, quasi-automated benchmark (available electronically as Supporting information ) for parametrization and validation of more approximate methods (such as DFT functionals and composite methods). Secondary contributions such as relativity can be included or omitted at will, unlike with experimental data. A broad variety of more approximate methods is assessed against the W4-11 benchmark and recommendations are made.

Peroxiredoxins (Prx) are thiol peroxidases that exhibit exceptionally high reactivity toward peroxides, but the chemical basis for this is not well understood. We present strong experimental evidence that two highly conserved arginine residues play a vital role in this activity of human Prx2 and Prx3. Point mutation of either ArgI or ArgII (in Prx3 Arg-123 and Arg-146, which are ∼3–4 A or ∼6–7 A away from the active site peroxidative cysteine (Cp), respectively) in each case resulted in a 5 orders of magnitude loss in reactivity. A further 2 orders of magnitude decrease in the second-order rate constant was observed for the double arginine mutants of both isoforms, suggesting a cooperative function for these residues. Detailed ab initio theoretical calculations carried out with the high level G4 procedure suggest strong catalytic effects of H-bond-donating functional groups to the Cp sulfur and the reactive and leaving oxygens of the peroxide in a cooperative manner. Using a guanidinium cation in the calculations to mimic the functional group of arginine, we were able to locate two transition structures that indicate rate enhancements consistent with our experimentally observed rate constants. Our results provide strong evidence for a vital role of ArgI in activating the peroxide that also involves H-bonding to ArgII. This mechanism could explain the exceptional reactivity of peroxiredoxins toward H2O2 and may have wider implications for protein thiol reactivity toward peroxides.

A benchmark calculation of the atomization energy of the ‘simple’ organic molecule C 2 H 6 (ethane) has been carried out by means of W4 theory. While the molecule is straightforward in terms of one-particle and n -particle basis set convergence, its large zero-point vibrational energy (and anharmonic correction thereto) and nontrivial diagonal Born–Oppenheimer correction (DBOC) represent interesting challenges. For the W4 set of molecules and C 2 H 6 , we show that DBOCs to the total atomization energy are systematically overestimated at the SCF level, and that the correlation correction converges very rapidly with the basis set. Thus, even at the CISD/cc-pVDZ level, useful correlation corrections to the DBOC are obtained. When applying such a correction, overall agreement with experiment was only marginally improved, but a more significant improvement is seen when hydrogen-containing systems are considered in isolation. We conclude that for closed-shell organic molecules, the greatest obstacles to highly accurate computational thermochemistry may not lie in the solution of the clamped-nuclei Schrodinger equation, but rather in the zero-point vibrational energy and the diagonal Born–Oppenheimer correction.