Present Density Functional Theory Research Articles

Theoretical prediction of low-energy photoelectron spectra of AlnNi- clusters (n = 1-13).

Mixed-metal clusters have long been studied because of their peculiar properties and how they change with cluster size, composition, and charge state and their potential roles in catalysis. The characterization of these clusters is therefore a very important issue. One of the main experimental tools for characterizing their electronic structure is photoelectron spectroscopy. Theoretical computation completes the task by fully determining the structural properties and matching the theoretical predictions to the measured spectra. We present density functional theory computations of the structural, magnetic, and electronic properties of negatively charged mixed AlnNi- clusters with up to 13 Al atoms. The lowest energy structures of the anionic clusters with up to 7 atoms are also found to be low-energy isomers of the neutral counterparts found in the literature. The 13-atom cluster is found to be a quartet and a perfect icosahedron. The predicted photoelectron spectra are also presented and can be used to interpret future experimental data. We also presented indicators that can be used to determine the potential of these systems for single-atom catalysis. These indicators point to smaller clusters to be more reactive as the gap between the Fermi energy and the center of the d-band increases with cluster size and that Ni occupies an internal site for n = 11-13. We speculate that reactivity can be enhanced if one adds an additional Ni atom. The DFT calculations were performed using the Becke exchange and Perdew-Wang/91 correlation functionals (BPW91), a DFT-optimized all-electron basis set for the aluminum atom, and the Stuttgart small core pseudopotential for the Ni atom. All of the computations used the Gaussian 03 software.

DFT combined to Boltzmann transport theory for optoelectronic and thermoelectric properties investigations for Se (4 & 8 (at.%)) doped Li2SnS3

Cubic Li2SnS3 emerges as a noteworthy ionic conductor and a viable electrode material for lithium secondary batteries. Its application extends to solar cell technologies, owing to its commendable optoelectronic properties and high-power conversion efficiency. In this study, we present density functional theory (DFT)-based first principles calculations for Li2SnS3-xSex (x = 0, 4, and 8% (atomic percent (at.%)) utilizing the modified Becke Johnson (mBJ) approximations, proposing a compelling alternative. Our investigation reveals significant optical absorption in the ultraviolet region for Li2SnS3-xSex (x = 0, 4, and 8%), accompanied by modest effective mass and indirect band gaps of 2.18 eV for the pristine material. Conversely, doped materials exhibit direct band gaps, with values of 2.113 eV for 4% and 2.026 eV for 8%. Furthermore, the calculated thermoelectric power factor underscores the potential and efficacy of Li2SnS3-xSex in thermoelectric energy devices. The findings not only highlight the material’s promise for solar applications but also underscore its candidacy as a novel solid-state electrolyte for lithium-ion batteries. This stems from its robust thermal stability and notable lithium-ion conductivity, positioning Li2SnS3 as a compelling candidate for advanced energy storage technologies.

Theoretical and experimental study of flower-like NiMoS/NiO/NF with interface layer as a novel highly efficient bifunctional-electrode toward supercapacitor and HER

Electrocatalytic water splitting and supercapacitor systems are considered one of the most imperative sustainable energy storage and conversion technologies as an alternative clean energy carrier/source to fossil fuels in order to address the pressing global warming problems. For achieving sustainable electrochemistry devices, highly efficient and superior durability electrocatalysts must be prepared through a facile and controllable approach. This study successfully demonstrated the development of a binder-free 3D- flower-like amorphous structure composite with self-assembled nanosheets supported on Nickel foam (NiMoS/NiO/NF) by a simple two-step hydrothermal technique as advanced electrocatalysts for alkaline hydrogen evolution reaction (HER) and supercapacitor. The as-obtained NiMoS/NiO/NF only needs a overpotential of 43 mV vs. RHE to reach 10 mA.cm−2 and remained stable after long-term HER tests. In the following, the nanostructure was operated as an electrode in the supercapacitor. According to the Galvanostatic Charge-Discharge (GCD) teats, the specific capacitance of NiMoS/NiO/NF was measured as 999F/g. Such outstanding NiMoS/NiO/NF performance can be ascribed to the synthesis of the interface layer (NiO), which makes the robust adhesion between NF and the final layer (NiMoS). The amorphous morphology with multi-component doping and heterojunctions, optimizes the hydrogen desorption sites, which leads to significant HER catalytic activity. The present experimental results and density functional theory (DFT) study offer a cost-effective, and convenient pathway to produce highly efficient non-nobel-based metal as high-valued multifunctional materials.

DFT computation of the electron spectra of thiophene

Recent experiments on thiophene using synchrotron radiation stimulated the present density functional theory (DFT) study of the various types of electron spectroscopy using the DFT methods we developed in our laboratory. Besides the confirmation of the experimental interpretations, the results of the present study strongly validate the methods used for the various types of electron spectroscopy. The average absolute deviations of the DFT results for thiophene from experiment are 0.22 eV for vertical ionization energies of outer valence electrons, 0.10 eV for carbon 1s binding energies, 0.19 eV for vertical valence excitation energies, and 0.18 eV for X-ray absorption energies. The calculated carbon 1s binding energies for bithiophene and terthiophene are also within 0.1 eV of synchrotron experiment. We conclude that workers using synchrotron radiation to study electronic processes of gas-phase molecules can apply our DFT methods for the interpretation of their experimental results.

Exploring hydrogen storage capabilities of boron nitride nanoring through density functional theory

AbstractThis study presents Density Functional Theory (DFT) investigation into the hydrogen storage capabilities of B6N6 nanoring. Utilizing the ωB97XD functional and def2TZVP basis set, this research explores the geometric, energetic, and electronic properties of the B6N6 nanoring, highlighting its potential as an efficient material for hydrogen storage. In‐depth analyses of the HOMO‐LUMO electronic density, Natural Bond Orbital (NBO) charge, Non‐Covalent Interactions (NCI), and Density of States (DOS) are conducted to understand the electronic structure changes during hydrogen adsorption. Furthermore, the desorption temperatures of hydrogen from the B6N6 nanoring, as calculated through the Van't Hoff equation, fall within a range considerably higher than the critical point of hydrogen. This finding indicates the practical feasibility of the B6N6 nanoring in hydrogen storage applications. Notably, the hydrogen storage capacity, measured in terms of gravimetric density, shows a significant increase with the addition of hydrogen molecules, reaching a maximum of 9.77% for 8H2 adsorbed on B6N6. Overall, this study underscores the B6N6 nanoring as a promising candidate for addressing the current challenges in hydrogen storage, particularly in terms of capacity, stability, and operational temperature.

193Ir nuclear forward scattering of an iridium(I) complex

Synchrotron based nuclear forward scattering (NFS) experiments using the 193Ir nucleus have been performed for the first time on a dinuclear iridium(I) complex, [IrCl(COD)]2 with COD being cycloocta-1,5-diene. This complex serves as a catalyst for hydrogenation and other chemical reactions. Both, the obtained absolute values of the isomer shift δ=0.87mm s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta =0.87 \\ {\ ext{mm s}}^{-1}$$\\end{document} and the quadrupole splitting ΔEQ=3.82mm s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varDelta {E}_{Q}=3.82 \\ {\ ext{mm s}}^{-1}$$\\end{document} agree within the experimental error with values obtained via conventional 193Ir Mössbauer spectroscopy reported earlier (Gál M. et al. J. Radioanal. Nucl. Chem., 260 (1) 2004, 133). In addition, we present density functional theory (DFT) calculations of the complex yielding its electronic structure and related Mössbauer parameters.

Vanadium and tantalum doping of tin dioxide: a theoretical study.

The increasing demand of efficient optoelectronic devices such as photovoltaics has created a great research interest in methods to manipulate the electronic and optical properties of all the layers of the device. Tin dioxide (SnO2), due to his charge transport capability, high stability and easy fabrication is the main electron transport layer in modern photovoltaics which have achieved a record efficiency. While the wide band gap of SnO2 makes it an effective electron transport layer, its potential for other energy applications such as photocatalysis is limited. To further improve is conductivity and reduce its bandgap, doping or co-doping with various elements has been proposed. In the present density functional theory (DFT) study, we focus on the investigation of vanadium (V) and tantalum (Ta) doped SnO2 both in the bulk and the surface. Here we focus on interstitial and substitutional doping aiming to leverage these modifications to enhance the density of states for energy application. These changes also have the potential to influence the optical properties of the material, such as absorption, and make SnO2 more versatile for photovoltaic and photocatalytic applications. The calculations show the formation of gap states near the band edges which are beneficial for the electron transition and in the case of Ta doping the lowest bandgap value is achieved. Interestingly, in the case of Ta interstitial, deep trap states are formed which depending of the application could be advantageous. Regarding the optical properties, we found that V doping significantly increases the refractive index of SnO2 while the absorption is generally improved in all the cases. Lastly, we investigate the electronic properties of the (110) surface of SnO2, and we discuss possible other applications due to surface doping. The present work highlights the importance of V and Ta doping for energy applications and sensor applications.

Development and Assessment of Computational Models Detailing the Influence of Extra‐Framework Cations on the Local Structure, Stability and Structure‐Property Relationships in Geopolymers

AbstractThis study presents density functional theory based computational analysis of geopolymeric materials of varied Si:Al ratios and extra‐framework cations. Due to the absence of crystallinity and long‐range order in geopolymers, no standard molecular models are present for quantum chemical analysis of these materials. Therefore, computationally feasible molecular models conforming to experimental reports and constraints are developed that accounted for all combinatorially possible local structures in the material. The computational analysis conclusively proved the effect of Si:Al ratio and the identity of the extra‐framework cation on the stability of the material with Si:Al = 2:1 decorated with Ca2 + ions exhibiting the highest stability. No significant effect of local structure is observed on the stability of the systems. Insights into the stability and adsorption property are developed on the basis of partial charge distribution thereby providing the details on the effects of constituent elements on the structure‐property relationships in geopolymers.

Synergistic effect of Fe/Co-doping and electric field in Niobium Diboride for boosting hydrogen production

A primary concern towards achieving a robust and sustainable water-splitting strategy consists in the development and designing of non-precious hydrogen evolution electrocatalysts capable of operating at relatively high current densities. In the present density functional theory (DFT) based study, we explored and identified α-NbB2-based catalysts consisting of Borophene as graphene-like noble metal-free networks in Niobium-metal based networks, as promising catalysts for the hydrogen-evolution reaction (HER). Our results unveiled that Fe/Co covalent doping in α-NbB2{001} surface provides high-efficiency HER activity sites, namely, TNb-sites in Nb-terminated Fe/Co-NbB2{001} surface with the lowest ΔGH∗ Gibbs free energy value of about 0.264/0.278 eV, which further drops to a very optimal value in the range of ΔGH∗≤± 0.10 eV upon the implementation of an external electric field. Furthermore, it was also revealed that in contrast to the extensively used Pt-based surface catalysts, both α-NbB2 and Fe/Co-NbB2 catalysts can sustain consistently high catalytic activity for HER over a very large hydrogen coverage and thus ensure a large density of effective catalytic free sites.

2-dimensional biphenylene monolayer as anode in Li ion secondary battery with high storage capacity: Acumen from density functional theory

Energy storage methods are cardinal for the mitigation of intermittency of renewable energy and among many technologies available, Li-ion batteries (LIBs) dominate the market on the account of their significant attributes. However, there is still room for improvement in their performance for high-end applications. Modifying the anode material can significantly affect the overall battery performance. It becomes necessary to discover a satisfactory negative electrode for more productive Li ion batteries. The present density functional theory based work examines the potential of a novel, experimentally fabricated 2D monolayer, Biphenylene having sp2 carbon atoms arranged periodically in four, six, and eight-membered rings, for its application in LIBs as adequate anode. Phonon spectrum and ab initio molecular dynamics (AIMD) signify the dynamic and thermal stability of the nanosheet. The band structures and density of states reveal the metallic nature which is maintained after the Li (adatom) adsorption as well. The mean adsorption energies for subsequent loading of Li over the sheet vary from -0.44 to -0.15 eV. The appreciative interactions between the adatom and the monolayer are well authenticated by charge transfer analysis. The Biphenylene monolayer is observed to offer a low diffusion barrier of 0.23 eV for the Li atoms. High storage capacity of 1302 mAhg−1 (almost 3.5 times higher than that of marketable Graphite), a low voltage of 0.34 V, and low volume changes (less than 3%) are noticed. This comprehensive study authenticates the capability of the 2D carbonous Biphenylene sheet as a suitable LIB negative electrode.

Intramolecular O···H Hydrogen Bonding of Salicylic Acid: Further Insights from O 1s XPS and 1H NMR Spectra Using DFT Calculations.

Intramolecular hydrogen bonding (HB) is a complex phenomenon that extends beyond a simple valence event, affecting the core electrons of a molecule. Salicylic acid (SA) and its conformers provide an excellent model compound for studying intramolecular HB as the proton donor (H) and acceptor (O) can be toggled by rotating the C-O and C-C bonds to form up to seven potential conformers through various HB. In this study, we computationally investigated intramolecular interactions in SA conformers with and without such HB, by examining their calculated O 1s core electron-binding energy (CEBE) and 1H NMR chemical shifts validated using recent measurements. The quantum mechanically stable SA conformers are fully defined by three rotatable bonds in the compound, which are abstracted as SA(η1η2η3) digital structures, where ηi = 0 if the ηi angles match the most stable SA conformer (000) and ηi = 1 otherwise. Our findings suggest that the stability is dominated by the appearance of the intergroup intramolecular HB of Hp···O (where O is in the carboxylic acid functional group and Hp is the phenolic proton in -OHp), and η3 serves as a switch of such HB. As a result, the (η1η20) SA conformers containing such Hp···O HB are more stable than other SA conformers (η1η21) without such the Hp···O HB. The present density functional theory calculations reveal that this Hp···O HB results in splitting of the O 1s CEBEs of two hydroxyl groups (-OH) by up to 1 eV and deshielding the Hp proton 1H NMR (δHp) up to 11.68 ppm for the (η1η20) conformers. Without such Hp···O HB, the O 1s XPS binding energies of two -OH groups will be closely located in the same band, and the 1H NMR chemical shift of the Hp atom will be as small as an 4.09 ppm SA conformer [SA-G(101)]. The present study indicates that the O 1s CEBE splitting between two -OH groups serves as an indicator of the presence of the Hp···O HB in SA conformers, which is also supported by the 1H NMR results.

Electronic and Optical Properties of Alkaline Earth Metal Fluoride Crystals with the Inclusion of Many-Body Effects: A Comparative Study on Rutile MgF2 and Cubic SrF2

We conducted a systematic investigation using state-of-the-art techniques on the electronic and optical properties of two crystals of alkaline earth metal fluorides, namely rutile MgF2 and cubic SrF2. For these two crystals of different symmetry, we present density functional theory (DFT), many-body perturbation theory (MBPT), and Bethe–Salpeter equation (BSE) calculations. We calculated a variety of properties, namely ground-state energies, band-energy gaps, and optical absorption spectra with the inclusion of excitonic effects. The quantities were obtained with a high degree of convergence regarding all bulk electronic and optical properties. Bulk rutile MgF2 has distinguished ground-state and excited-state properties with respect to the other cubic fluoride SrF2 and the other members of the alkaline earth metal fluoride family. The nature of the fundamental gaps and estimates of the self-energy and excitonic effects for the two compounds are presented and discussed in detail. Our results are in good accordance with the measurements and other theoretical–computational data. A comparison is made between the excitation and optical properties of bulk rutile MgF2, cubic SrF2, and the corresponding clusters, for which calculations have recently been published, confirming strong excitonic effects in finite-sized systems.

Effects of Ga on the structural, mechanical and electronic properties of β-Ti-45Nb alloy by experiments and ab initio calculations

This work aims to investigate the structural, mechanical and electronic properties of four novel β-type (100-x)(Ti–45Nb)-xGa alloys (x = 2, 4, 6, 8 wt%) for implant applications by means of experimental and theoretical (ab initio) methods. All alloys retain the bcc β phase in the solution-treated and quenched state while the lattice parameter decreases with increase in Ga content. This is due to its smaller atomic radius compared to Ti and Nb, in line with the present density functional theory (DFT) calculations. Tensile and microhardness tests indicate a clear strengthening effect with increasing Ga content, with yield strengths in the range 551 ÷ 681 MPa and microhardness in the range 174 ÷ 232 HV0.1, mainly attributed to grain refinement and solid solution strengthening. Ga also positively affects ductility, with a maximum value of tensile strain at fracture of 32%. Non-destructive ultrasonic measurements and DFT calculations reveal that the bulk modulus is unaffected by the Ga presence. This phenomenon might be due to the fact that Ga introduced bonding and anti-bonding electron low energy states which balance the average bond strength among the atoms in the metallic matrix. Nevertheless, the introduction of new Ga–Ti super sp-like bonding orbitals along the [110] and [−110] directions in the Ga neighborhood could explain the increase of the Young's modulus upon Ga addition (73 ÷ 82.5 GPa) that was found experimentally in the present work. Hence, Ga addition to Ti–45Nb leads to a suitable balance between increased strength and low Young's modulus.

Understanding the effect of Ni and Co doping in magnetic properties of La0.7Ca0.3MnO3: Magnetic Compton spectroscopy and DFT strategies

Magnetic Compton profiles (MCPs) of La0.7Ca0.3Mn0.95(Ni/Co)0.05O3 between 8 and 250 K have been measured using high energy inelastic scattering at SPring-8, Japan. For a quantitative analysis on amendment of magnetic properties, temperature-dependent experimental MCPs are decomposed into constituent profiles related to Mn, Ni/Co and itinerant (diffuse) electrons. Decomposed profiles unambiguously show that Mn-3d electrons are ferromagnetically coupled with Ni/Co ions while itinerant electrons are linked anti-ferromagnetically with Mn-3d and Ni/Co-3d electrons. An annotation of MCP and VSM data depicts that the orbital magnetic moments are anti-ferromagnetically coupled to total spin moments. Variation in magnetic response in undoped and Ni/Co doped perovskites is devoted to formation of mixed valence states of Mn atom. The spin contribution at different sites are found to be in tune with present density functional theory (DFT) based calculations which are thoroughly analyzed on the basis of changes in the eg and t2g states of Mn, Ni/Co caused by Jahn-Teller distortion. Present MCP data and DFT calculations set guidelines to probe the reliable origin to examine magnetic response and half-metallic properties of such manganites.

Determination of layer charge density in expandable phyllosilicates with alkylammonium ions: A combined experimental and theoretical assessment of the method

Layer charge deficit is a key crystal-chemical parameter for the classification and nomenclature of 2:1 phyllosilicates that also controls some of their fundamental properties such as cation exchange capacity, expandability, water content, or rheology. The clay community has thus devoted significant efforts to determine this parameter either from the smectite/vermiculite chemical composition (the structural formula method) or experimentally using the alkylammonium method, that theoretically allows the determination of the mean layer charge density and of its distribution. In the present study density functional theory (DFT) and molecular dynamics (MD) simulations are compared to experimental X-ray diffraction data for a series of synthetic saponites with layer charge ranging from medium-charge smectite to medium-charge vermiculite. Consistency of computed and measured layer-to-layer distances confirms the ability of computational approaches to accurately predict the organization of alkylammonium cations in smectite interlayers. Thermalization of DFT-optimized structure models through MD simulations allows probing possible alternative interlayer configurations such as the electrostatically-favored location of ammonium heads above/below Al-substituted tetrahedra. X-ray diffraction results showed that layer-to-layer distances intermediate between those corresponding to the stable h1, h2, etc. interlayer configurations described in the literature result from the interstratification of different stable configurations. The overall consistency of computational and experimental results confirms also the ability of the alkylammonium method to accurately determine a mean value of layer charge density consistent with smectite structural formula when using the revised equations proposed by Laird et al. (1989). The validity of the method appears however limited to smectite-group minerals [layer charge density ranging from ~0.5 to ≤1.2 per O20(OH)4] most likely owing to the coexistence of both stable “layered” and paraffin-like interlayer configurations for higher values of layer charge. In addition, this consistency challenges the ability of the method to quantitatively describe distributions of layer charge in expandable phyllosilicates even when using the complete series of alkylammonium cations.

Photodegradation of dye using Polythiophene/ZnO nanocomposite: A computational approach

Incorporating nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. Here, we present density functional theory (DFT) study of Polythiophene/Zinc oxide (PTh/ZnO) nanocomposite with high photocatalytic performance and stability which exhibits superior degradation of alizarine dye under the visible light condition with interaction energy of −149.55 kcal/mol between conducting polymer (PTh) and metal oxide, with PTh sponsoring more number of electrons to the conduction band of ZnO. The electrical and optical properties of optimized geometries of PTh/ZnO nanocomposite were studied by frontier molecular orbital analysis, natural bond orbital (NBO) charge simulation, natural electronic configuration, and UV–vis absorption spectra. The modulation of the energy band gap (∽ 2.60 eV) and exciton binding energy (∽ 0.36 eV) causes visible light absorption and hence enhances the photodegradation activity of PTh/ZnO. NBO analysis evidences the electron accepting behavior of ZnO in the composites as it withdraws electron cloud density of about 0.14e from the polymer unit.

Mechanism of oscillation of aqueous electrical double layer capacitance: Role of solvent

The present classical density functional theory (CDFT) study is focused on role of solvent in differential capacitance (Cd) behavior of aqueous electrolyte electric double-layer capacitor (EDLC). In the CDFT, water molecule is described by a solvent primitive model, which is constructed to give two experimentally measured aandb parameters in the van der Waals equation of state of water; Lennard-Jones parameters of both cation and anion are chosen to be reminiscent of properties of K+ andCl-1; a structureless and soft wall comprised of carbon atoms is considered to represent a graphene electrode. Main findings are summarized as follows. (i) The CdH (H is separation between two graphene electrodes) curve is always shifted up (at lower electrode voltage) or down (at higher electrode voltage) by increasing the electrolyte bulk concentrationc. The anomalous negative correlation between c and Cd at high voltage originates from the so-called charge inversion and one additional weak co-ion peak located closer to the electrode surface at higher voltage. (ii) Oscillation periods of CdH curves are basically fixed at 3 Å regardless of molecular characteristics of counter- and co-ions, c value, and electrode voltage; explicit consideration of the solvent granularity and polarity greatly reduces the attenuation rate of the oscillation with pore size. Increase of CdH with pore size reducing towards the ion size, does occur but only with moderate magnitude; a main CdH extreme value occurs approximately around H being two times ion diameter, which can be either a maximum or a minimum, depending on electrolyte bulk concentration, polarity and strength of the electrode. These oscillation features differ greatly from those observed in solvent-free ionic liquids and continuum solvent model. (iii) Potential of zero charge ψpzc for the case of small size of cation and weaker LJ interaction of the cation with solvent molecule in large number, is necessarily positive and its value is positively correlated with the c value; minimum point ψMin of the Cdψs curve is always larger than theψpzc, not consistent with the Gouy-Chapman theory, and both the ψpzcH curve and ψMinH curve change quasi periodically with the pore size H also in 3 Å cycle. (iv) Theoretical analysis shows that the capacitance behavior is mainly controlled by the number and position of solvent peaks and their changes with pore size, while distribution of ions is largely controlled by their LJ interaction with solvent. This shows the importance of the solvent in modulating the capacitance behavior.

Thermodynamic and Kinetic Studies on Copper-Catalyzed Cross-Dehydrogenative Couplings of N-Aryl Glycine Esters with Phenols

Abstract Copper-catalyzed cross-dehydrogenative coupling (CDC) reactions have been esteemed as a straightforward and efficient tool for C–C bonds formation. The single electron transfer (SET) process plays a vital role during the overall catalytic cycle. In the present density functional theory (DFT) study on the oxidation potential (Eox), which could reflect the SET occurring tendency from a thermodynamic respect as well as the substituent effects and structure-activity relationships for four classes of N-based compound substrates including THIQs, N,N-dimethylanilines, 3-benzylindoles, and N-phenylglycine esters derivatives have been fulfilled. Many quantitative structure-activity relationships between Eox and structural parameters, including HOMO energies, the Hammett substituent constant σ+ and so on were found. Furthermore, in the kinetics research section, we have performed four possible pathways of CDC reaction of N-aryl glycine esters with phenols in a CuBr/TBHP catalytic oxidation system. The results support the pathway wherein the formation of an iminium cation-type intermediate is involved would be more favorable. In addition, the solvent and substituent effects of two key steps including H-abstraction and C–C bond formation rate-determining step were explored, which could afford a total understanding of the mechanism regarding the Cu-catalyzed CDC reaction as well as the substrates and solvents screening.

Insertion of the Liquid Crystal 5CB into Monovacancy Graphene.

Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by defects that are introduced, either by design or as a byproduct of fabrication processes. Herein, we present density functional theory (DFT) calculations of the LC mesogen 4-cyan-4′-pentylbiphenyl (5CB) on graphene in the presence of a monovacancy (MV-G). We find that the monovacancy strengthens the binding of 5CB in the planar alignment and that the structure is lower in energy than the corresponding homeotropic structure. However, if the molecule is able to approach the monovacancy homeotropically, 5CB undergoes a chemical reaction, releasing 4.5 eV in the process. This reaction follows a step-by-step process gradually adding bonds, inserting the 5CB cyano group into MV-G. We conclude that this irreversible insertion reaction is likely spontaneous, potentially providing a new avenue for controlling both LC behavior and graphene properties.

Investigation of CO and OH adsorption and oxidation in the presence of cocatalytic ruthenium ions on the Pt(111) surface

We present Density Functional Theory (DFT) calculations for COads adsorption and COads + OHads ➔ CO2 + Hads reactions on a Pt(111) slab with, and without, adsorbed RuCl5. CO stretching frequencies and bond distances between CO and PtC were calculated. The derived activation energies and reaction energies provide strong evidence that the OHads on the Pt(111) surface oxidatively remove COads in a kinetically more facile manner in the presence of co-adsorbed RuCl5. Methanol catalytic activation by cocatalytic RuCl5 ions offers a promising and convenient route to implementing a methanol-feed with trace levels of Ru ions under fuel cell operating conditions.