Chemical Bond Analysis Research Articles

High-Throughput Screening for Advanced Thermoelectric Materials: Diamond-Like ABX2 Compounds.

High-throughput (HTP) calculations are a highly promising direction for the discovery of novel functional materials. Here we use an HTP framework to investigate the electronic structures and p-type thermoelectric properties of the ABX2 compounds with diamond-like structures. We show application of HTP both to identify compounds and also to identify underlying trends. A total of 65 entries out of 84 908 in the Materials Informatics Platform are selected for this study. The electronic structures and chemical-bonding analyses reveal that there exists a general conductive network consisting of the anion X sublattice, which dominates the electrical transport properties of the compounds. Electrical and thermal transport properties of the 41 pnictide and chalcogenide compounds with sufficient band gaps are studied. Pnictide compounds have relatively smaller Seebeck coefficients than the chalcogenide compounds. This is due to the smaller effective masses around the valence band maxima. The electrical conductivities and power factors, however, are better in pnictide compounds. This is because pnictide compounds have high electronic group velocities and electronic relaxation times. Combined with the predictions of lattice thermal conductivities based on the Slack model, 12 novel p-type and n-type ABX2 materials with high ZT values are predicted.

Possible lower energy isomer of carbon clusters Cn (n = 11, 12) via particle swarm optimization algorithm: Ab initio investigation

The low energy structures of neutral carbon clusters Cn (n = 11, 12) are predicted by means of particle swarm optimization and quantum chemistry calculation. The energy and geometrical structure of these isomers are further optimized by DFT, MP2 and CCSD computation methods. The relative Gibbs free energy below 5000 K was calculated, which indicates that C11 clusters are more sensitive to temperature. We also illustrate the computational simulated IR spectra obtained at B3LYP/cc-pVTZ level, which shown the vibrational modes and vibrational regions of different structural isomers. Combining nuclear independent chemical shift (NICS) and harmonic oscillator measure of aromaticity (HOMA), we have analyzed the aromaticity of the three single-ring structures and found that C11 cluster is not aromatic, while the ground stated structure of C12 is anti-aromaticity. Chemical bond analysis of the ground state is performed by Adaptive Natural Density Partition (AdNDP) injunction with electron localization function (ELF), it is found that the 2c-2e bonds of C11 and C12 planar ring structures presented strong and weak alternations, respectively, and their multi-central bonds were strongly dependent on the symmetry of molecular configuration. Finally, topological and natural bond orbital (NBO) analysis indicate that there is no electrostatic interaction in the Cn (n = 11, 12) clusters, and the high angular momentum orbital has a primary contribution to negative natural valance electron configuration. From the electronic configuration, we can see that the natural hybridized orbit of C11 and C12 clusters is mainly composed of sp hybrids.

Correlations between Density-Based Bond Orders and Orbital-Based Bond Energies for Chemical Bonding Analysis.

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals. Another important parameter reflecting the nature and strength of a chemical bond is the bond order that can be assessed by the density derived electrostatic and chemical (DDEC6) method which relies on an electron and spin density-partitioning scheme. Herein, we describe a linear correlation that can be established between the DDEC6-derived bond orders and the bond strengths computed with the COHP formalism. We demonstrate that within defined boundaries, the COHP-derived bond strengths can be consistently compared among each other and linked to the DDEC6-derived bond orders independent of the used model. The validity of these correlations and the effective model independence of the electronic descriptors are demonstrated for a variety of gas-phase chemical systems, featuring different types of chemical bonds. Furthermore, the applicability of the derived correlations to the description of complex reaction paths in periodic systems is demonstrated by considering the zeolite-catalyzed Diels–Alder cycloaddition reaction between 2,5-dimethylfuran and ethylene.

Chemical bonding analysis of excited states using the adaptive natural density partitioning method.

A novel approach to chemical bond analysis for excited states has been developed. Using an extended adaptive natural density partitioning method (AdNDP) as implemented in AdNDP 2.0 code, we obtained chemically intuitive bonding patterns for the excited states of H2O, B5+, and C2H4+ molecules. The deformation pathway in the excited states could be easily predicted based on the analysis of the chemical bond pattern. We expect that this new method of chemical bonding analysis would be very helpful for photochemistry, photoelectron spectroscopy, electron spectroscopy and other chemical applications that involved excited states.

Flexible iron-doped Sr(OH)2 fibre wrapped tuberose for high-performance supercapacitor electrode

The fiber wrapped tuberose structured Fe:Sr(OH)2 have been successfully deposited by using a simple and low cost chemical approach of successive ion layer adsorption and reaction (SILAR) method as binder-free electrodes for supercapacitors. The structural properties have been obtained by the XRD patterns, while FTIR shows the chemical bond analysis. The FE-SEM micrographs show fiber wrapped tuberose structured morphology and the Fe doping into Sr(OH)2 is confirmed by EDX. The deposited films show the battery type electrode behaviour in 1 M Na2SO4 aqueous solution. As an active electrode material, the specific capacity of 871 C g−1 (specific capacitance of 792 F g−1) at 1.2 mA cm−2 with cycle retention of ∼79% at 5 mA cm−2 has been obtained for 0.5 at.% Fe:Sr(OH)2. The electrochemical properties of the synthesised electrode reveal that it has the great potential for next-generation energy storage applications.

Influence of Cu on the Performance of Tuberose Architecture of Strontium Hydroxide Thin Film as a Supercapacitor Electrode

AbstractA simple, economical successive ionic layer adsorption and reaction (SILAR) method has been used for synthesizing 1, 2 and 3 at.% copper‐doped strontium hydroxide over a stainless‐steel (SS) substrate. X‐ray diffraction reveals the orthorhombic crystal structure of polycrystalline Cu‐doped Sr(OH)2. FTIR and Raman analyses explore the chemical bond analysis of the active material. The morphology of the Cu‐doped Sr(OH)2 was analyzed by using SEM. This shows novel hierarchical‐branched tuberose with flakes. The energy‐dispersive X‐ray spectroscopy (EDAX) also confirms the doping of Cu into Sr(OH)2. The electrochemical properties have been investigated by using cyclic voltammetry (CV) and galvanostatic charge−discharge measurements. It has been perceived that doping clearly affects the supercapacitive behavior. The specific capacity of the 3 at.% Cu‐doped Sr(OH)2 film electrode exhibits a maximum specific capacity of 817 C g−1 at 0.4 mA cm−1 in 1 M Na2SO4 electrolyte, but has a low cycle stability. The 2 at.% Cu‐doped sample shows high cycle stability by retrieving 71 % of its capacity after 5000 cycles. The relationship between the doping concentration and supercapacitive behavior has also been discussed. The good capacitive behavior and cycle stability of the Cu‐doped Sr(OH)2 gives the new perspective for the flexible electrode material, which can be used in the near future as an energy storage material.

Controlled Crystal Growth of Indium Selenide, In2Se3, and the Crystal Structures of α-In2Se3.

In2Se3 has been known for over 100 years and recently attracted interest as a promising candidate for a variety of applications, such as solar cells, photodiodes, and phase-change memories. Despite the broad concern for possible uses, its polymorphism and structure are poorly characterized. By combining X-ray diffraction, transmission electron microscopy, and quantum-chemical calculations, we present here the crystal structures of two layered room-temperature polytypes: 3R and 2H In2Se3. Both polymorphs are stacking variants of the same Se-In-Se-In-Se layers comprising two coordination environments for the In atoms, one tetrahedral and one octahedral. By using chemical-bonding analysis, we look at the different In positions in α-In2Se3 and compare them to those in the metastable β-phase.

The relationship between covalent bonds and the optical response in a nonpolar family ATeMoO6 (A=Mg, Zn, Cd): A Berry-phase investigation

The macroscopic polarization, the refractive indices, birefringence, and the second-order nonlinear optical susceptibilities in a family of nonpolar materials ATeMoO6 (A = Mg, Zn, and Cd) have been investigated using the Berry-phase calculation. The microscopic origin of the optical response is further investigated by the variation of atomic charge, the Born effective charges, and the chemical bond analyses based on the Bader charge analysis and the Mulliken bond population analysis. The results show that the robust covalent bonds play an important role in determining the refractive indices and SHG response, and the anisotropic electron distributions on covalent Te‒O and Mo‒O bond give main contribution to the optical anisotropic birefringence.

Synthesis, structure and antioxidant performance of boron nitride (hexagonal) layers coating on carbon nanotubes (multi-walled)

Carbon nanotube/Boron nitride(CNT/BN) nanocomposites were performed by a facile method with boric acid (H3BO3) and melamine (C3H6N6). Uniform boron nitride (BN) precursor deposition films were deposited onto the surface of multiwall carbon nanotubes (MWCNTs),which involves attachment of the precursor and subsequent nitridation in ammonia atmosphere at 1050 °C. The qualitative and quantitative analysis of X-ray diffraction (XRD) on the crystal structure and phase composition. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the material surface morphology and coating structure. Chemical composition analysis of surface and chemical bonds formed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared Spectroscopy (FTIR) confirmed as well as the oxidation resistance under high temperature by thermal gravimetric analysis and differential thermal analysis (TG-DTA). The results indicate that the boron nitride coating on carbon nanotubes composite has been synthesized successfully by this method and greatly improves the antioxidant performance of carbon nanotubes compared with the original carbon nanotubes (690 °C, compared to 550 °C of original carbon nanotubes), which provides a potential application at high temperatures for carbon nanotube materials.

Spindle nodal chain in three-dimensional α' boron.

Topological metals/semimetals (TMs) have emerged as a new frontier in the field of quantum materials. A few two-dimensional (2D) boron sheets have been suggested as Dirac materials, however, to date TMs made of three-dimensional (3D) boron structures have not been found. Herein, by means of systematic first principles computations, we discovered that a rather stable 3D boron allotrope, namely 3D-α' boron, is a nodal-chain semimetal. In momentum space, six nodal lines and rings contact each other and form a novel spindle nodal chain. This 3D-α' boron can be formed by stacking 2D wiggle α' boron sheets, which are also nodal-ring semimetals. In addition, our chemical bond analysis revealed that the topological properties of the 3D and 2D boron structures are related to the π bonds between boron atoms, however, the bonding characteristics are different from those in the 2D and 3D carbon structures.

Synthesis, Crystal Structure, and Chemical-Bonding Analysis of BaZn(NCN)2

The ternary carbodiimide BaZn(NCN)2 was prepared by a solid-state metathesis reaction between BaF2, ZnF2, and Li2NCN in a 1:1:2 molar ratio, and its crystal structure was determined from Rietveld refinement of X-ray data. BaZn(NCN)2 represents the aristotype of the LiBa2Al(NCN)4 structure which is unique to carbodiimide/cyanamide chemistry and is well regarded as being constructed from ZnN4 tetrahedra, sharing edges and vertices through NCN2− units to form corrugated layers with Ba2+ in the interlayer voids. Structural anomalies in the shape of the cyanamide units are addressed via IR spectrometry and DFT calculations, which suggest the presence of slightly bent N=C=N2− carbodiimide units with C2v symmetry. Moreover, chemical-bonding analysis within the framework of crystal orbital Hamilton population (COHP) reveals striking similarities between the bonding interactions in BaZn(NCN)2 and SrZn(NCN)2 despite their contrasting crystal structures. BaZn(NCN)2 is only the second example of a ternary post-transition metal carbodiimide, and its realization paves the way for the preparation of analogues featuring divalent transition metals at the tetrahedral Zn2+ site.

Theory of Three-Electrone Bond in the Four Works with Brief Comments (Notes)

Note 1. Three-electrone bond it is an existing particle (object). Note 2. Chemical bond - it is the interaction of fermions. Note 3. Alternative description of the chemical bond. Note 4. Urea molecule. Note 5. Oxygen. Note 6. Chemical bond - is a new indivisible particles. Note 7. Model of the Interfering Universe.

Automated Transition State Search and Its Application to Diverse Types of Organic Reactions.

Transition state search is at the center of multiple types of computational chemical predictions related to mechanistic investigations, reactivity and regioselectivity predictions, and catalyst design. The process of finding transition states in practice is, however, a laborious multistep operation that requires significant user involvement. Here, we report a highly automated workflow designed to locate transition states for a given elementary reaction with minimal setup overhead. The only essential inputs required from the user are the structures of the separated reactants and products. The seamless workflow combining computational technologies from the fields of cheminformatics, molecular mechanics, and quantum chemistry automatically finds the most probable correspondence between the atoms in the reactants and the products, generates a transition state guess, launches a transition state search through a combined approach involving the relaxing string method and the quadratic synchronous transit, and finally validates the transition state via the analysis of the reactive chemical bonds and imaginary vibrational frequencies as well as by the intrinsic reaction coordinate method. Our approach does not target any specific reaction type, nor does it depend on training data; instead, it is meant to be of general applicability for a wide variety of reaction types. The workflow is highly flexible, permitting modifications such as a choice of accuracy, level of theory, basis set, or solvation treatment. Successfully located transition states can be used for setting up transition state guesses in related reactions, saving computational time and increasing the probability of success. The utility and performance of the method are demonstrated in applications to transition state searches in reactions typical for organic chemistry, medicinal chemistry, and homogeneous catalysis research. In particular, applications of our code to Michael additions, hydrogen abstractions, Diels-Alder cycloadditions, carbene insertions, and an enzyme reaction model involving a molybdenum complex are shown and discussed.

Synthesis, Characterization, and Chemical Bonding Analysis of the Lithium Alkaline‐earth Metal Gallide Nitrides Li2(Ca3N)2[Ga4] and Li2(Sr3N)2[Ga4

Large single crystals of Li2(Ca3N)2[Ga4] and Li2(Sr3N)2[Ga4] up to several mm in size were grown from mixtures of the respective elements and binary alkaline‐earth metal nitrides in reactive lithium melts employing a modified high‐temperature centrifugation‐aided filtration (HTCAF) technique. The main structural features of these isotypic phases are stella quadrangula building units [Ga4]Li4/2 and octahedra (Nae6/2), which form two independent interpenetrating networks. The phases crystallize in the η‐carbide structure and represent diamagnetic small bandgap semiconductors. Real‐space chemical bonding analysis indicates predominantly ionic bonding.

The Role of Auxiliary Alkali Metal Ions on Scheelite Structure Double Molybdate and Tungstate Phosphors.

Eu3+-doped alkali metal double molybdate and tungstate phosphors, (MEu) (Mo,WO4)2 (MEM and MEW, M = Li+, Na+, and K+), have been identified as potential candidate materials for white light-emitting diodes. However, there are no systematic considerations of the role of auxiliary alkali-metal ions (AMIs) on the structural, chemical, and luminescent properties of these phosphors. Here, a systematic investigation to elucidate the role of AMIs on MEM and MEW phosphors was performed using ab initio calculations based on experimental evidence. The results from experimental assessments with intensive structural and chemical bond analyses reveal a clear dependence of AMIs on the structural and luminescent properties of phosphors. The structural changes due to AMIs originate from a bond length change between AMIs-O2- bonds, and AMIs had minor effects on the other bonds. A phase transition induced by K+ ions originates from not only structural factors but also local chemical bonding characteristics. Overall, the results indicate that the major role of AMIs is to induce phosphor structural changes, and the effects on the chemical properties are minor. The results of this study shed light on developing not only MEM and MEW phosphors but also new phosphor materials using auxiliary metal ions.

Microscopic analysis of AgCl polymorphism

A detailed theoretical study of the structural properties of the phases involved in the pressure-induced polymorphic sequence of AgCl is reported. As many other binary ionic compounds, AgCl crystallizes in the B1 (NaCl-type) structure at ambient pressure and shows a high-pressure B2 (CsCl-type) structure under pressure. However, unlike alkali halides, there is not a direct transformation from one to the other. The greater polarizability of the silver chloride structure enables the stabilization of two other phases in between B1 and B2: the monoclinic (KOH-type) and the orthorhombic (TlI-type, B33) structures. This polymorphic sequence is specially interesting, since a concerted transition pathway within the monoclinic KOH-type symmetry has also been proposed as a transition pathway in the B1 → B2 transformation. This would point at a connection between symmetries that are thermodynamically and kinetically stabilized, with phases that appear under pressure being good candidates for mechanistic analyses. Our calculations yield cell parameters and structural behavior under pressure in overall good agreement with available experimental data for all these phases and extend the information previously observed for the four polymorphs (e.g., compressibilities). Computed transition pressures confirm the B1→KOH-type→B33 sequence. In order to analyze the occurrence of the KOH-type phase between the B1 and B33 phases, we have resorted to the Atoms In Molecules approach to obtain the evolution of charges with pressure. We find that the descent to the KOH-type symmetry provides a continuous change in ionic charges between B1 and B33 phases, which implies a smaller stress. Thus, coupling group–subgroup relationships to chemical bond analysis can provide microscopic insight into why a given symmetry is favored.

Bonding analyses of unconventional carbon allotropes

Utilizing first-principles electronic-structure calculations, we present the chemical-bonding analyses of hypothetical carbon allotropes based on tetrahedral structure motifs such as T-carbon, TY-carbon and T-graphene. While previous publications on these novel allotropes have dealt with ab initio phonon, band structure and DOS calculations, the focus of this work is the partitioning of the band-structure energy in terms of bonding, nonbonding and antibonding contributions. We re-evaluate the chance of making such allotropes by careful bond analyses and compare them to already known equivalents, namely diamond, graphene and the Buckminsterfullerene molecule. A synthetic route is proposed to a new compound, called TY-carbodiimide, that exhibits similar structure and bonding properties as TY-carbon.

Hydrogen trapping in MAX phase Ti3SiC2: Insight from chemical bonding by density functional theory

Understanding hydrogen (H) isotope trapping in materials is essential to optimize the material performance in a nuclear environment for the fabrication of nuclear devices. By using the density functional theory (DFT), herein we have systematically investigated the behaviour of hydrogen in the MAX phase Ti3SiC2 in the presence and absence of a vacancy (V). When a vacancy is generated in a favorable plane for hydrogen accumulating (Si plane), two distinct behavours of hydrogen in the Si plane have been identified by chemical bond analysis, i.e., the Ti-H and Si-H bonding, which synergistically results in VH2 complexes prevailing in the host matrix. Different from metals and other ceramics, the trapping mechanism of H in Ti3SiC2 essentially originates from the spatially inhomogeneous distribution of free-charge density and large discrepancy of electronegativity between the host atoms. Our theoretical results offer great insights into the rational design of new high-performance nuclear materials.

Diffusion and thermite reaction process of film-honeycomb Al/NiO nanothermite: Molecular dynamics simulations using ReaxFF reactive force field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374217 and 21363019).

The diffusion and thermite reaction process of Al/NiO nanothermite composed of Al nanofilm and NiO nano honeycomb are investigated by molecular dynamics simulations in combination with the ReaxFF. The diffusion and thermite reaction are characterized by measuring energy release, adiabatic reaction temperature, and activation energy. Based on time evolution of atomic configuration and mean square displacement, the initialization of the thermite reaction process of Al/NiO nanothermite results from the diffusion of Al atoms. Under the microcanonical ensemble, it is found that the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite reaches over 5500 K, and activation energy is 8.43 kJ/mol. The release energy of the thermite reaction process of Al/NiO nanothermite is 2.2 kJ/g, which is in accordance with the available experimental value. With the same initial temperature, the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite has a tendency to decrease dramatically as the equivalence ratio increases. On the basis of chemical bond analysis, the initial temperature and equivalence ratio have great effects on the thermite reaction process, but do not significantly affect the average length of Al–Ni nor Al–O bond. Overall, the thermite reaction of film-honeycomb Al/NiO nanothermite is a complicated process instead of a theoretical equation.

Chemical Bonding Analysis as a Guide for the Preparation of New Compounds: The Case of VIrGe and HfPtGe.

The chemical bonding of transition metal compounds with a MgAgAs-type of crystal structure is analyzed with quantum chemical position-space techniques. The observed trends in QTAIM Madelung energy and nearest neighbor electron sharing explain the occurrence of recently synthesized MgAgAs-type compounds, TiPtGe and TaIrGe, at the boundary to the TiNiSi-type crystal structure. These bonding indicators are used to identify favorable element combinations for new MgAgAs-type compounds. The new phases-the high-temperature VIrGe and the low-temperature HfPtGe-showing this type of crystal structure are prepared and characterized by powder X-ray diffraction and differential thermal analysis.