Bond Energy Terms Research Articles

Effect of Sasobit warm mix on micro properties of asphalt with different degrees of regeneration

In this work, an aged asphalt was mixed with a new modified asphalt based on styrene–butadiene–styrene (SBS) in different proportions, and the warm mixing agent was added to simulate the asphalt fusion behaviour in the warm mixed recycled asphalt with different aged asphalt fertilizer (reclaimed asphalt pavement, RAP) content. Low field nuclear magnetic resonance (LF-NMR), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR) were used as analytical techniques to study the role of the warm mixing agent in terms of molecular bond energy, apparent morphology, and functional groups. It was found that the softening point and penetration of asphalt are reduced, and the ductility is increased, during the regeneration process. Sasobit warm mix agent can reduce the penetration and ductility of asphalt and improve the softening point. Its viscosity reduction effect is mainly achieved by adsorbing saturated components and decreasing the bond energy between 1H and other molecules; Sasobit warm mix agent can improve the aging state of mixed asphalt. On the AFM two-dimensional adhesion diagram, the number of bee-shaped structures and the single area is reduced; in the new and old mixed asphalt, the greater the proportion of new asphalt, the more evident the effect of Sasobit warm mix agent is.

A Bond-Energy/Bond-Order and Populations Relationship.

We report an analytical bond energy from bond orders and populations (BEBOP) model that provides intramolecular bond energy decompositions for chemical insight into the thermochemistry of molecules. The implementation reported here employs a minimum basis set Mulliken population analysis on well-conditioned Hartree-Fock orbitals to decompose total electronic energies into physically interpretable contributions. The model's parametrization scheme is based on atom-specific parameters for hybridization and atom pair-specific parameters for short-range repulsion and extended Hückel-type bond energy term fitted to reproduce CBS-QB3 thermochemistry data. The current implementation is suitable for molecules involving H, Li, Be, B, C, N, O, and F atoms, and it can be used to analyze intramolecular bond energies of molecular structures at optimized stationary points found from other computational methods. This first-generation model brings the computational cost of a Hartree-Fock calculation using a large triple-ζ basis set, and its atomization energies are comparable to those from widely used hybrid Kohn-Sham density functional theory (DFT, as benchmarked to 109 species from the G2/97 test set and an additional 83 reference species). This model should be useful for the community by interpreting overall ab initio molecular energies in terms of physically insightful bond energy contributions, e.g., bond dissociation energies, resonance energies, molecular strain energies, and qualitative energetic contributions to the activation barrier in chemical reaction mechanisms. This work reports a critical benchmarking of this method as well as discussions of its strengths and weaknesses compared to hybrid DFT (i.e., B3LYP, M062X, PBE0, and APF methods), and other cost-effective approximate Hamiltonian semiempirical quantum methods (i.e., AM1, PM6, PM7, and DFTB3).

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

New insight into the electronic structure of SiF4: synergistic back-donation and the eighteen-electron rule.

SiF4 demonstrated high thermal stability in dry air or vacuum, and a Si-F bond length of 1.554 Å is close to the second period element C-C bond length (1.54 Å) of C2H6. To determine which factors confer this property of SiF4, here we conduct a comparative study of a series of molecules SiHnF4-n (n = 0, 1, 2, 3), SiX4 (X = Cl, Br, I), CF4 and TiF4 in terms of bond length and energy, molecular orbitals, and adaptive natural density partitioning (AdNDP) analysis. The AdNDP analysis shows that there are five 5c-2c bonds in SiF4, here named synergistic back-donation (SBD) bonds. These SBD bonds together with the Si-F σ bonds and the eighteen-electron rule are demonstrated as the main factors contributing to the short Si-F bond length and the high thermal stability of SiF4 in dry air or vacuum. Moreover, the SBD bonds exist widely in other isoelectronic species of SiF4 such as ClO4-, SO42-, PO43- and XeO4.

Charge density waves in multiple- Q spin states

Coupling between spin and charge degrees of freedom in electrons is a source of various electronic and magnetic properties of solids. We theoretically study charge density waves induced by the spin-charge coupling in the presence of magnetic orderings in itinerant magnets. By performing a perturbative calculation in the weak-coupling limit of the Kondo lattice model, we derive a useful formula for the relationship between charge and spin density waves, which can be applied to any magnetic orderings, including noncollinear and noncoplanar ones composed of multiple spin density waves called multiple-$Q$ magnetic orderings. We demonstrate the predictive power for single-$Q$ and double-$Q$ states including skyrmion and meron-antimeron crystals on a square lattice, in comparison with the numerical calculations. Moreover, we show that the charge density waves contain richer information than the spin density waves, and are indeed useful in distinguishing the spin textures with similar spin structure factors. We discuss the relation to bond modulation in terms of the kinetic bond energy and the vector spin chirality. We also perform numerical calculations beyond the perturbative regime and find that the charge density waves can be enhanced when the electron filling is commensurate. Furthermore, we investigate the effect of the spin-orbit coupling, which can lead to additional charge density waves owing to effective anisotropic magnetic interactions in momentum space. Our result will provide a way to identify complex magnetic orderings and their origins from the charge modulations.

From Electronegativity towards Reactivity-Searching for a Measure of Atomic Reactivity.

Pauling introduced the concept of electronegativity of an atom which has played an important role in understanding the polarity and ionic character of bonds between atoms. We set out to define a related concept of atomic reactivity in such a way that it can be quantified and used to predict the stability of covalent bonds in molecules. Guided by the early definition of electronegativity by Mulliken in terms of first ionization energies and Pauling in terms of bond energies, we propose corresponding definitions of atomic reactivity. The main goal of clearly distinguishing the inert gas atoms as nonreactive is fulfilled by three different proposed measures of atomic reactivity. The measure likely to be found most useful is based on the bond energies in atomic hydrides, which are related to atomic reactivities by a geometric average. The origin of the atomic reactivity is found in the symmetry of the atomic environment and related conservation laws which are also the origin of the shell structure of atoms and the periodic table. The reactive atoms are characterized by degenerate or nearly degenerate (several states of the same or nearly the same energy) ground states, while the inert atoms have nondegenerate ground states and no near-degeneracies. We show how to extend the use of the Aufbau model of atomic structure to qualitatively describe atomic reactivity in terms of ground state degeneracy. The symmetry and related conservation laws of atomic electron structures produce a strain (energy increase) in the structure, which we estimate by use of the Thomas-Fermi form of DFT implemented approximately with and without the symmetry and conservation constraints. This simplified and approximate analysis indicates that the total strain energy of an atom correlates strongly with the corresponding atomic reactivity measures but antibonding mechanisms prevent full conversion of strain relaxation to bonding.

Study of optical parameters of sulphur doped Se-As thin films as optical materials

A conventional thermal evaporation technique has been used for thin film preparation of Se40As60−ySy (y = 0, 10, 20) chalcogenide materials. Optical characterization has been done in the wavelength range of 600–2700 nm in the thin films of above mentioned materials. Various optical parameters like refractive index, extinction coefficient, dielectric constant, dielectric loss, absorption coefficient and band gap have been calculated after the analysis of transmission spectra of the given samples. On the basis of optical parameters the optical characteristics have been discussed for Se40As60−ySy (y = 0, 10, 20) materials. Optical band gap is estimated by using Tauc’s extrapolation and is found to increase with S addition. This behavior of optical band gap is interpreted in terms of co-ordination number and chemical bond energy. The outcomes of optical characterization motivated towards to find the scope of present glassy system as optical materials.

Recent progress of bismuth vanadate-based photoelectrocatalytic water splitting

<p indent=0mm>With increasing energy demands and ever-growing environmental concerns, solar energy and hydrogen energy have attracted worldwide attention. In particular, hydrogen energy not only has a high energy density, but also is clean, renewable, and carbon-free, when compared with primary energy sources such as coal, oil, and natural gas and secondary energy sources such as coal gas, petrol, and diesel. Photoelectrocatalytic (PEC) water splitting for hydrogen generation is a process in which a PEC cell containing photoelectrodes and electrolyte is used to split water into hydrogen and oxygen by solar energy. Therefore, PEC water splitting is one of the ideal ways to covert and store solar energy to hydrogen energy in terms of chemical bond energy. In a PEC cell, the photoanode is commonly based on n-type semiconductors and the photocathode based on p-type semiconductors. The efficiency of a PEC cell is determined by performance of these photoelectrodes interfaced with the electrolyte. However, because the oxygen evolution reaction on the photoanode is kinetically sluggish involving four electrons and the valance band maximum of photoanodes must be more positive than <sc>1.23 V</sc> versus reversible hydrogen electrode, suitable n-type semiconductors are quite few for this purpose, limiting the common photoanodes to low efficiencies for PEC water splitting. In recent years, the bismuth vanadate photoanode has attracted great attention due to its relatively high theoretical maximum photocurrent density <sc>(~7 mA cm^–2)</sc> and suitable band structure for water splitting, compared with other traditional photoanodes such as titanium dioxide, tungsten oxide, and zinc oxide. Extensive efforts have been made to unleash the full potential of the bismuth vanadate photoanode for PEC water splitting. In this mini review, we survey and analyze the design ideas and synthesis methods of high-performance bismuth vanadate photoanodes by looking back at the research progress made over the past few years on improving the light harvesting efficiency, photo-generated carrier separation efficiency and surface oxygen evolution efficiency of bismuth vanadate photoanodes. The strategies for improving the efficiencies of the bismuth vanadate photoanodes include defect state introduction, crystal facet and morphology control, and heterojunction engineering. Among the strategies, a single one, such as the defect state introduction, may enhance efficiencies of several processes (e.g., photo-generated carrier separation efficiency and surface oxygen evolution efficiency) of bismuth vanadate at the same time, but sometimes, it may enhance the efficiency of one process but degrade the efficiencies of others for the bismuth vanadate photoanode. Thus, how to comprehensively consider the cooperative mechanism to enhance the efficiencies of all the processes involved in PEC water splitting is the key to obtaining high performance bismuth vanadate photoanodes. At present, bismuth vanadate-based photoanodes have exhibited an extremely high photocurrent density and photo-generated carrier separation efficiency at higher bias voltage (over <sc>5 mA cm^–2</sc> at <sc>1.23 V</sc> versus reversible hydrogen electrode with over 90% photo-generated carrier separation efficiency), but the light reflection of bismuth vanadate-based photoanodes makes it unable to reach the theoretical maximum photocurrent density <sc>(~7 mA cm^–2).</sc> Moreover, the efficiencies of bismuth vanadate-based photoanodes at low bias voltages are still too low. Therefore, the future development direction should be to obtain higher photocurrent density at a lower voltage, and increase the absorption efficiency and wavelength range of bismuth vanadate to reach the theoretical photocurrent density and beyond. Although bismuth vanadate photoanodes are not necessarily the final large-scale application scheme of PEC water splitting in the future, their studies will help to provide guidelines for searching new high-performance photoanode materials.

Empirical Potential Energy Function Toward ab Initio Folding G Protein-Coupled Receptors.

Approximately 40-50 percent of all drugs targets are G protein-coupled receptors (GPCRs). Three-dimensional structure of GPCRs is important to probe their biophysical and biochemical functions and their pharmaceutical applications. Lacking reliable and high quality free function is one of the ugent problems of computational predicting the three-dimensional structure in this community. We proposed a GPCR-specified energy function composed of four novel empirical potential energy terms: a two-dimensional contact energy force field, knowledge-based helix pair connection distance energy term, knowledge-based helix pair angle restraint energy term and a disulfide bond energy term. To validate the energy function, we employed an ab initio GPCR three-dimensional structure predictor to test if the energy function improved the accuracy of prediction. We evaluated 28 solved GPCRs and found that 21(75 percent) targets were correctly folded (TM-score>0.5). Also, the average TM-score using the energy function was 0.54, which was improved 134 percent than the TM-score 0.23 for MODELLER energy function and 170 percent than the TM-score 0.20 for Rosetta membrane energy function. The results confirmed that our empirical potential energy function toward ab initio folding is competitive to state-of-the-art solutions for structural prediction of GPCRs.

The optical properties of a- (GeS2)100-xGax thin films

Thin films whose compositions can be expressed by (GeS2)100-xGax (x=0, 6,12,18) formula were obtained by thermal evaporation technique of bulk material at a base pressure of ~10-5 torr. Optical transmission spectra of the films were taken in the range of 300-1100 nm then the optical band gap, tail width of localized states, refractive index, extinction coefficient were calculated. The optical constants were found to increase at low concentration of Ga (0 to12%) while they decreases with further addition of Ga. The optical band gap was found to change in opposite manner to that of optical constants. The variation in the optical parameters are explained in terms of average bond energy of the system.

Crystallization behavior of Ge-Sb-Se glasses in the compositional range for use as molded lenses

We have investigated compositional dependences of crystallization events of Ge-Sb-Se glasses across the compositional range appropriate for molded lens applications in the long-wavelength infrared spectrum. The onset temperature of crystallization turned out to feature no significant dependence on compositional changes of the constituent atoms, unlike glass transition temperature, Vickers hardness and thermal expansion coefficient, all of which revealed a much more significant correlation against germanium or selenium content. In an effort to unveil glass-structural attributes to the observed onset temperature of crystallization values, both mean coordination number and average bond energy were taken into consideration: The onset temperature of crystallization values appeared to be linearly proportional to average bond energy, whereas no such a correlation was verified in the case of mean coordination number. We delineated these behaviors, with an emphasis paid to the off-stoichiometry of each glass composition, in terms of network connectivity and chemical bond energy of the glass structure. In addition, crystalline phases precipitated during the bulk crystallization were identified, and the effects of the surface crystallization were analyzed in connection with infrared transmittance and hardness.

A generalized Ising model for studying alloy evolution under irradiation and its use in kinetic Monte Carlo simulations

We derive an Ising Hamiltonian for kinetic simulations involving interstitial and vacancy defects in binary alloys. Our model, which we term ‘ABVI’, incorporates solute transport by both interstitial defects and vacancies into a mathematically-consistent framework, and thus represents a generalization to the widely-used ABV model for alloy evolution simulations. The Hamiltonian captures the three possible interstitial configurations in a binary alloy: A-A, A-B, and B-B, which makes it particularly useful for irradiation damage simulations. All the constants of the Hamiltonian are expressed in terms of bond energies that can be computed using first-principles calculations. We implement our ABVI model in kinetic Monte Carlo simulations and perform a verification exercise by comparing our results to published irradiation damage simulations in simple binary systems with Frenkel pair defect production and several microstructural scenarios, with matching agreement found.

Glass-forming ability and rigidity percolation in SeTePb lone-pair semiconductors

Correlating the various physical parameters of known semiconductors and pointing the properties of new ones, a number of parameters have been employed recently with different levels of success. Taking this into account an attempt has been made to correlate the physical properties of Pb-doped Se–Te lone-pair semiconductors. The small band gap and large Bohr radius of lead (Pb) containing lone-pair semiconductors assist them with specific optical, electrical and thermal properties. The various physical parameters like number of constraints, lone pair of electron, heat of atomization, density, compactness, free volume percentage have been analyzed in terms of mean coordination number for (Se90Te10)100−x Pb x (x = 0, 4, 8, 12, 16, 20, 24). The band gap for the compositions has been determined theoretically, and the obtained results are very well explained in terms of cohesive energy, electronegativity and average single bond energy.

Quantum-chemical modeling of strength of organometallic bonds in oil

Metal–organics bond dissociation energies in compounds modeling different metal-containing structures in oil have been calculated using ab initio quantum-chemical methods. It has been found that bond energies calculated by the cbs-qb3, b3lyp/dgdzvp, and b3lyp/cc-pVDZ methods for diatomic molecules are arranged in the order: E(M–O) > E(M–S), E(M–C) > E(M–N), where M = V, Ni, or Co. Vanadium oxide VO in the vanadyl porphyrin molecule has been shown to possess the strongest bond (277.4 kcal/mol). Sandwiched structures are also stable: by using the ub3lyp/6-31g(d,p) method, the decomposition energy of the sandwich (C5H5)2M = M + 2C5H5 has been estimated and equals at 260.2 kcal/mol for M = Fe or 141.0 kcal/mol for M = Ni. The electronic structure of transition metal (M = V, Ni, Fe) complexes with π-conjugated bonds of benzene, pyrrole, and pyridine molecules has been calculated using the ub3lyp/6-31g(d) method. The thermal stability of the complexes has been discussed in terms of bond energy.

Effect of γ-irradiation on the optical and electrical properties of PbxGe42−xSe48Te10

The composition dependence of optical and electrical of amorphous unirradiated and γ-irradiated thin films of PbxGe42-xSe48Te10 (5≤x ≤16) deposited by thermal evaporation was measured as a function of wavelength (0.3μm≤λ≤2.5μm). The optical transition was found to be indirect. The optical energy gap (Eopt) decreases with increasing concentration of Pb at.wt.% and exhibits a minimum value for the composition with 9 at.wt.% Pb and the results have been interpreted in terms of the average bond energy. The band tail (Ec) obeys Ubarch's empirical relation. The d.c. electrical resistance was measured in a temperature range of (300–455K). The activation energy for electrical conduction decreased with increasing Pb concentration. The electronic conduction in the temperature range has been attributed to band transport mechanism. The effect of γ-radiation on the optical constants (n, k), band tail (Ec) and Eelect energies as a function of composition has been determined. The results show that, the radiation causes increase in optical and electrical energies as γ-doses increase.

Assessment of the flotation activity of reagents in terms of the hydrogen bond energy in molecular complexes with active sites of the coal surface

The hydrogen bond energy of molecular complexes between a flotation reagent and coal’s organic mass is calculated for the first time. The electron density distribution in molecules of 2-methyl-1,3-dioxane and 2-methyl-1,3-dioxa-2-silacyclohexane is determined. It is shown that the silicon atom in the molecule of 2-methyl-1,3-dioxa-2-silacyclohexane increases the electron density at oxygen atoms from −0.279 to −0.424 and −0.432 in positions 1 and 3 of the molecule, respectively. This increases the hydrogen bond energy of the reagent in molecular complexes with water and model compounds of the coal’s organic mass. In molecular complexes of 2-methyl-1,3-dioxa-2-silacyclohexane with model compounds of the coal’s organic mass, the hydrogen bond energy is considerably higher than in corresponding complexes of 2-methyl-1,3-dioxane. As a result, the adsorption of 2-methyl-1,3-dioxa-2-silacyclohexane on the coal surface is 35–45% greater than for 2-methyl-1,3-dioxane. Consequently, the coal grains become more hydrophobic, and their flotation is improved. With the same consumption of reagents, the use of 2-methyl-1,3-dioxa-2-silacyclo-hexane rather than 2-methyl-1,3-dioxane increases the concentrate yield and reduces the losses of the coal’s organic mass with the wastes. Analogous flotation properties of coal are found for other cyclic acetals and their silicon analogs. Experimental data confirm that the hydrogen bond energy in complexes between the flotation reagent and the coal’s organic mass may be used to assess its effectiveness.

Glass transition and crystallization kinetics analysis of Sb–Se–Ge chalcogenide glasses

Differential thermal analysis (DTA) has been employed to investigate the effect of Ge addition on the glass transition behavior and crystallization kinetics of Sb10Se90−xGex (x = 0, 19, 21, 23, 25, 27) alloys. The three characteristic temperatures viz. glass transition (T g), crystallization (T c), and melting (T m) have been determined and found to vary with the heating rates and Ge content. Thermal stability and glass forming tendency have been evaluated in terms of ΔT (= T c − T g) and reduced glass transition temperature. The activation energies for glass transition and crystallization have been used to analyze the nucleation and growth process. The activation energy analysis also determines the suitability of alloys to be used in switching applications. Results have been interpreted in terms of bond energies and structural transformations in the investigated alloys.

Atomic site preferences and its effect on magnetic structure in the intermetallic borides M2Fe(Ru0.8T0.2)5B2 (M=Sc, Ti, Zr; T=Ru, Rh, Ir)

The site preference for a class of intermetallic borides following the general formula M2Fe(Ru0.8T0.2)5B2 (M=Sc, Ti, Zr; T=Ru, Rh, Ir), has been explored using ab initio and semi-empirical electronic structure calculations. This intermetallic boride series contains two potential sites, the Wyckoff 2c and 8j sites, for Rh or Ir to replace Ru atoms. Since the 8j site is a nearest neighbor to the magnetically active Fe atom, whereas the 2c site is a next nearest neighbor, the substitution pattern should play an important role in the magnetic structure of these compounds. The substitution preference is analyzed based on the site energy and bond energy terms, both of which arise from a tight-binding evaluation of the electronic band energy, and are known to influence the locations of atoms in extended solids. According to these calculations, the valence electron-rich Rh and Ir atoms prefer to occupy the 8j site, a result also corroborated by experimental evidence. Additionally, substitution of Rh or Ir at the 8j site results in a modification of the magnetic structure that ultimately results in larger local magnetic moment on the Fe atoms.

Low-strain interface models for epitaxial graphene on SiC(0001)

A set of low-strain commensurate interface structures for epitaxial graphene on SiC(0001) are obtained by combining rotated graphene supercells with m×m or m3×m3R30° SiC cells. For two among the interfaces with lowest strain, corresponding to 4×4 and 63×63R30° SiC periodicities, we analyze the binding energy of the graphene/SiC(0001) interface in terms of bond energies resulting from the (partial) saturation of individual Si dangling bonds by C atoms of graphene. These bond energies are determined as a function of the relative lateral displacement between the surface Si atoms and the graphene honeycomb. We find that this model energy does not explain the variation of the binding energies obtained from direct density functional calculations for the full interfacial systems. Moreover, for a given interface, the lateral rearrangements of the Si and C atomic positions found upon relaxation do not lead to any significant increase of the model binding energy. These results indicate that the deformations of the graphene layer cannot be neglected in the modeling of the binding energy of the graphene/SiC(0001) system.

Stabilities of complex compounds of metals in non-aqueous solutions

By defining the successive stability constants of metal complex compounds in terms of generalised equilibria it is possible to study metals which do not form simple hydrated metal ions and also non-water soluble ligands and complexes. If the equilibrium constants are to be interpreted in terms of bond energies etc. it is necessary that the system be defined. That is, the real compositions of the compounds in the equilibrium solution should be known. Some important types of interfering dissociations and reactions can be detected by means of electrical conductivity measurements and some results of such measurements are outlined. The system [PdCl2 (n-C8H17NH2)2] + PBu3n = [PdCl2 (n-C8H17NH2) (PBu3n) ] +C8H17NH2 [PdCl2 (n-C8H17NH2) (PBu3n)] + PBu3n = [PdCl2(PBu3n)2] + C8H17NH2 has been studied and the free energy changes for the replacement of n-octylamine by tri-n-butylphosphine in the two stages are: ΔG1 = −4.56 to −5.08 kcal. ΔG2 =−5.30 to −5.92 kcal.