Chemical Bond Order Research Articles

Tensile mechanical characteristics of ultra-thin carbon sulfur nanothreads in orientational order

Carbon sulfur nanothreads (CSNTs) mainly composed of two chiral long alkane chains have been recently fabricated from thiophene by a pressure-induced phase transition in low-temperature, but their mechanical properties remain unexplored. Here, the critical roles of morphology and temperature on the tensile characteristics of CSNTs are for the first time examined using molecular dynamic simulations with a first-principles-based ReaxFF forcefield. It is revealed that CSNTs exhibit high tensile Young's modulus, high tensile strength and excellent ductility, and their tensile properties are morphology and temperature dependent. Morphologically, atomic arrangement with various configurations makes every CSNTs possess unique mechanical properties. Thermally, as temperature varies from 1 to 1500 K, CSNTs become mechanically weakened. In comparison with conventional diamond nanothreads (DNTs) and carbon nitride nanothreads (CNNTs), CSNTs show distinct axial elongation mechanisms, with relatively insignificant changes in chemical bond orders and bond length in the skeleton prior to the final rupture. Instead, the stretching of bond angle and dihedral angle mainly contribute to the global axial elongation, while the torsional deformation is limited due to their perfect global symmetry in the configuration. This study provides fundamental insights into the mechanics of ultra-thin CSNT structures.

Atomic force microscopy probes fractional differences in chemical bond order

High-resolution images can map out subtle variations in a molecule’s electronic and geometric structure.

Imaging fractional differences in chemical bond order

High-resolution atomic force microscopy can map out subtle variations in a molecule’s electronic structure.

Amorphous Ge15Te85: density functional, high-energy x-ray and neutron diffraction study

The structure and electronic properties of amorphous Ge15Te85 have been studied by combining density functional (DF) simulations with high-energy x-ray and neutron diffraction measurements. Three models with 560 atoms have been constructed using reverse Monte Carlo methods constrained to (1) agree with the experimental structure factors S(Q), and have (2) energies close to the DF minimum and (3) a semiconducting band structure. The best structure is based on the melt-quenched DF structure and has a small number of Ge–Ge bonds. It shows interlocking networks of Te and GeTe with a significant fraction (22–24%) of voids (cavities). Ge occurs with both tetrahedral and 3 + 3 defective octahedral configurations, and the coordination of Te is slightly higher than indicated by the ‘8 − N rule’ (N is the number of valence electrons). The GeTe network includes clusters of ABAB squares (A = Ge, B = Te), and the bonding is characterized by the chemical bond orders.

Molecular conductance in relation to inverse transport theory and to chemical bond order

AbstractMcCaskill and March (MM) have derived a resistivity theory in the form of a quotient, the numerator of which is a force–force correlation function. The denominator has the form 1 − b, where MM forge a link between the quantity b and bound states. Evidently, as b tends to unity, one approaches a metal‐insulator transition, which has potential relevance for molecular conductance. In addition, Klein was involved in early work in this area, in which contact is established with chemical bond order. Practical examples of this are discussed in this article. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Calculation of σ-, π-, and δ-components of quantum-chemical bond orders

Wiberg (WAB) and Mayer (BАВ) indexes introduced and theoretically proved in the 1960-80s [1–5] are widely used as quantum-chemical analogs of the chemical bond order or multiplicity. These indexes are cal-culated on the basis of a density matrix by a uniform algorithm for any molecules and types of bonds that allows analysis of chemical bonds in compounds of various compositions and structures. The indexes take the values close to 1, 2, or 3 in the cases when these values are assigned to the bonds by the classical structural theory. The concept of a multiplicity of the chemical bond is inseparably linked to the isolation of its σ-, π-, and δ-components. These components are easy to find for linear molecules by sorting their МОs by irreducible representations of the C∞v or D∞h point groups [6]. Meanwhile, σand π-bonds between atoms are discussed in the chemical literature also for molecules with different geometrical structures, for which such classification of МОs is impossible.

DFT study of metastable linkage isomers of six-coordinate ruthenium nitrosyl complexes

Abstract The linkage isomers of the [M(NO)(CN)5]2− (M = Fe, Ru, Os), [Ru(NO)Cl5]2−, trans-[Ru(NO)(NH3)4(L)]q+ (L = NH3, H2O, nicotinamide, imidazole, pyridine, pyrazine, NO2 −, OH−, Cl−), and trans-[Ru(NO)L4(OH)]q (L = pyridine, NO2 −) ions are studied by density functional theory. DFT calculations show that the electronic ground-state potential surface of these nitrosyl complexes has the local minima corresponding to η 2-NO and η 1-O linkage isomers, of which the former is characterized by lower energy. The stationary points on the ground state potential energy surface along the GS → MS2 → MS1 path for the [M(NO)(CN)5]2− (M = Fe, Ru, Os) and [Ru(NO)Cl5]2− complexes were found. The calculations of infrared spectra of linkage isomers [Ru(NO)Cl5]2− and [Ru(NO)(CN)5]2− are carried out. The analysis of quantum chemical bond orders indicates a noticeable delocalization of π-electron density along the Ltrans—M—NO axis and a possibility of direct interactions between NO and equatorial ligands in the structures with the bent {MNO} group.

Topological index-quantum chemical bond order relations

In this work the molecular connectivity indices calculated and are weighted by Mulliken and Lowdin (in parentheses) bond orders. We considered six simple hydrocarbons (ethane, ethene, propane, propene, 2-methylpropane, and 2-methlypropene) to try to relate these values to a physical property (in this paper to molecular volume) in order to establish a relation between the quantities.

Sigma Bonded Radical Cation Complexes: A Theoretical Study

A theoretical study on the nature of bonding in several weakly bound radical cation complexes from second and third row hydrides is presented. It is shown that characterization of a two-center three-electron or 2c−3e bond based on its bond distance and binding energy may be misleading in many cases. It is also observed that the ab inito quantum chemical bond order index cannot be taken as a definite signature of a 2c−3e bond. Instead, it is suggested that appropriate localized molecular orbital need be used to test the presence of a 2c−3e bond. Localization of relevant molecular orbital in the 2c−3e bonded systems also suggests that the newly formed bond is of sigma character. Normal-mode analysis is performed to identify the stretching mode in the 2c−3e bonded radical cation complexes. Geometry optimizations are carried out at MP2 and restricted open shell Becke's half-and-half (BHH) nonlocal exchange and Lee−Yang−Parr (LYP) nonlocal correlation functionals (BHHLYP) with 6-31++G(d,p) basis set. Hessian c...

Quantum chemical bond order as a local descriptor for modelling reaction paths

The feasibility of studying chemical reactions by focusing attention only on the bonds actively involved in the reaction process is explored. Active bond order (BO) profiles are shown frequently to be characterized by the occurrence of sharp inflexions at a point close to the saddle point on the reaction path. The sum of the active BOs is shown to remain approximately conserved. Active BOs may therefore be used as a local descriptor of the reaction path. This leads to extended bond-energy bond-order (EBEBO) postulates which are proposed to transcribe an essentially local picture of a reaction as a superposition of elementary chemical events into a semi-global description. A local Hammond postulate and its ramifications are explored along with a local measure of the asynchronicity of the bond-breaking and bond-making processes in a chemical reaction. The origin of BO inflexions is theoretically sought to be connected with Fermi correlation.

Handling of intrinsic divergence in the orthogonal gradient method of orbital optimization in an MC-SCF framework and geometry optimization in pathological cases: I (propynal in excited states)

It is demonstrated that a generalized version of the orthogonal gradient method of orbital optimization may sometimes encounter a specific divergence problem which may be termed intrinsic to the first order method. Instead of switching over to a more sophisticated second order method one can cure the divergence problem at the first order level itself by suitably tailoring the MC-SCF operator or the MC-SCF energy matrix. Results of complete geometry optimization of propynal inl,3nπ* and3ππ* states (pathological cases) are reported to demonstrate the usefulness of the method at an INDO-MCSCF level of approximation. The results of structure calculations are further rationalized from generalized quantum chemical bond order indices.

Theoretical studies of hydride transfer reactions

AbstractThe intersecting‐state model (ISM) has been applied to the study of hydride transfer reactions between variously substituted and elaborated pyridinium ions in solution. Chemical bond order is conserved along the reaction coordinate, with a transition state bond order of n≠ = 0·5. This supports the view that these reactions have essentially a synchronous nature and occur by thermal activation over an energy barrier. Tunnelling of H− is negligible because the effective mass for the solvated species is high. Reaction energy and kinetic isotope effects are well accounted for by the model. For reactions in the vapour phase, ISM and the tunnel effect theory show that tunnelling becomes the dominant mechanism. The same is also valid for proton transfers in the vapour phase.

The behavior of quantum chemical bond order in the vicinity of a saddle point on the reaction path

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe behavior of quantum chemical bond order in the vicinity of a saddle point on the reaction pathD. K. Maity and S. P. BhattacharyyaCite this: J. Am. Chem. Soc. 1990, 112, 8, 3223–3225Publication Date (Print):April 1, 1990Publication History Published online1 May 2002Published inissue 1 April 1990https://doi.org/10.1021/ja00164a060RIGHTS & PERMISSIONSArticle Views83Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (391 KB) Get e-Alerts Get e-Alerts

Chemical bond order in the MO LCAO method. The approximation of zero differential overlap (ZDO)

Chemical bond order in the MO LCAO method. The approximation of zero differential overlap (ZDO)