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Sample records for initio valence bond

  1. Resonance and Aromaticity : An Ab Initio Valence Bond Approach

    NARCIS (Netherlands)

    Rashid, Zahid; van Lenthe, Joop H.; Havenith, Remco W. A.

    2012-01-01

    Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB wav

  2. Resonance and aromaticity: an ab initio valence bond approach.

    Science.gov (United States)

    Rashid, Zahid; van Lenthe, Joop H; Havenith, Remco W A

    2012-05-17

    Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB wave function for each system was constructed using a linear combination of the VB structures (spin functions), which closely resemble the Kekulé valence structures, and two types of orbitals, that is, strictly atomic (local) and delocalized atomic (delocal) p-orbitals, were used to describe the π-system. It is found that the Pauling-Wheland's resonance energy with nonorthogonal structures decreases, while the same with orthogonalized structures and the total mean resonance energy (the sum of the weighted off-diagonal contributions in the Hamiltonian matrix of orthogonalized structures) increase when delocal orbitals are used as compared to local p-orbitals. Analysis of the interactions between the different structures of a system shows that the resonance in the 6π electrons conjugated circuits have the largest contributions to the resonance energy. The VBSCF calculations also show that the extra stability of phenanthrene, a kinked benzenoid, as compared to its linear counterpart, anthracene, is a consequence of the resonance in the π-system rather than the H-H interaction in the bay region as suggested previously. Finally, the empirical parameters for the resonance interactions between different 4n+2 or 4n π electrons conjugated circuits, used in Randić's conjugated circuits theory or Herdon's semi-emprical VB approach, are quantified. These parameters have to be scaled by the structure coefficients (weights) of the contributing structures.

  3. Modern ab initio valence bond theory calculations reveal charge shift bonding in protic ionic liquids.

    Science.gov (United States)

    Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo

    2016-06-21

    The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties.

  4. An ab initio Valence Bond Study on Cyclopenta-Fused Naphthalenes and Fluoranthenes

    NARCIS (Netherlands)

    Havenith, R.W.A.; van Lenthe, J.H.; Jenneskens, L.W.

    2005-01-01

    To probe the effect of external cyclopenta-fusion on a naphthalene core, ab initio valence bond (VB) calculations have been performed, using strictly atomic benzene p-orbitals and p-orbitals that are allowed to delocalize, on naphthalene (1), acenaphthylene (2), pyracylene (3), cyclopenta[b,c]-acena

  5. The new Resonating Valence Bond Method for ab-initio Electronic Simulations

    CERN Document Server

    Sorella, Sandro

    2013-01-01

    The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.

  6. Ab initio determination of bond length dependence of the correlated valence shell Hamiltonian of CH: Comparison with semiempirical theories

    Science.gov (United States)

    Sun, Hosung; Freed, Karl F.

    1984-01-01

    The exact ab initio effective valence shell Hamiltonian, which is mimicked by semiempirical theories of valence, is calculated for CH at 11 bond lengths using quasidegenerate many-body perturbation theory to incorporate extensive correlation contributions. Least squares fits of the bond length dependence of the calculated CH matrix elements provide simple formulas which are compared with the intuitive forms introduced into semiempirical theories. Some of the semiempirical formulas, e.g., one-center, one-electron integrals and two-center, two-electron integrals, are in good agreement with our correlated ab initio calculations, while others display substantial departures. For example, the bond length dependence of one-center, two-electron integrals, which are assumed to be independent of bond length in semiempirical theories, is substantial but physically understandable. Corrections are found to the assumed proportionality of resonance and overlap integrals. The bond length dependence of nonclassical three-electron integrals is presented along with the hybrid and exchange integrals that are ignored in zero differential overlap methods.

  7. Ab initio valence calculations in chemistry

    CERN Document Server

    Cook, D B

    1974-01-01

    Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge

  8. Combining quantum wavepacket ab initio molecular dynamics with QM/MM and QM/QM techniques: Implementation blending ONIOM and empirical valence bond theory.

    Science.gov (United States)

    Sumner, Isaiah; Iyengar, Srinivasan S

    2008-08-07

    We discuss hybrid quantum-mechanics/molecular-mechanics (QM/MM) and quantum mechanics/quantum mechanics (QM/QM) generalizations to our recently developed quantum wavepacket ab initio molecular dynamics methodology for simultaneous dynamics of electrons and nuclei. The approach is a synergy between a quantum wavepacket dynamics, ab initio molecular dynamics, and the ONIOM scheme. We utilize this method to include nuclear quantum effects arising from a portion of the system along with a simultaneous description of the electronic structure. The generalizations provided here make the approach a potentially viable alternative for large systems. The quantum wavepacket dynamics is performed on a grid using a banded, sparse, and Toeplitz representation of the discrete free propagator, known as the "distributed approximating functional." Grid-based potential surfaces for wavepacket dynamics are constructed using an empirical valence bond generalization of ONIOM and further computational gains are achieved through the use of our recently introduced time-dependent deterministic sampling technique. The ab initio molecular dynamics is achieved using Born-Oppenheimer dynamics. All components of the methodology, namely, quantum dynamics and ONIOM molecular dynamics, are harnessed together using a time-dependent Hartree-like procedure. We benchmark the approach through the study of structural and vibrational properties of molecular, hydrogen bonded clusters inclusive of electronic, dynamical, temperature, and critical quantum nuclear effects. The vibrational properties are constructed through a velocity/flux correlation function formalism introduced by us in an earlier publication.

  9. Valence-Bond Theory and Chemical Structure.

    Science.gov (United States)

    Klein, Douglas J.; Trinajstic, Nenad

    1990-01-01

    Discussed is the importance of valence bond theory on the quantum-mechanical theory of chemical structure and the nature of the chemical bond. Described briefly are early VB theory, development of VB theory, modern versions, solid-state applications, models, treatment in textbooks, and flaws in criticisms of valence bond theory. (KR)

  10. The chemical bond in inorganic chemistry the bond valence model

    CERN Document Server

    Brown, I David

    2016-01-01

    The bond valence model is a version of the ionic model in which the chemical constraints are expressed in terms of localized chemical bonds formed by the valence charge of the atoms. Theorems derived from the properties of the electrostatic flux predict the rules obeyed by both ionic and covalent bonds. They make quantitative predictions of coordination number, crystal structure, bond lengths and bond angles. Bond stability depends on the matching of the bonding strengths of the atoms, while the conflicting requirements of chemistry and space lead to the structural instabilities responsible for the unusual physical properties displayed by some materials. The model has applications in many fields ranging from mineralogy to molecular biology.

  11. Bond valence at mixed occupancy sites. I. Regular polyhedra.

    Science.gov (United States)

    Bosi, Ferdinando

    2014-10-01

    Bond valence sum calculations at mixed occupancy sites show the occurrence of systematic errors leading to apparent violations of the Valence Sum Rule (bond valence theory) in regular and unstrained bonding environments. The systematic deviation of the bond valence from the expected value is observed in the long-range structure, and is discussed from geometric and algebraic viewpoints. In the valence-length diagram, such a deviation arises from discrepancies between the intersection points of the long-range bond valences and the theoretical bond valences with the valence-length curves of involved cations. Three factors cause systematic errors in the bond valences: difference in atomic valences, bond valence parameters Ri (the length of a bond of unit valence) and bond valence parameters bi (the bond softness) between the involved cations over the same crystallographic site. One important consequence strictly related to the systematic errors is that they lead to erroneous bond strain values for mixed occupancy sites indicating underbonding or overbonding that actually does not exist.

  12. Seniority Number in Valence Bond Theory.

    Science.gov (United States)

    Chen, Zhenhua; Zhou, Chen; Wu, Wei

    2015-09-01

    In this work, a hierarchy of valence bond (VB) methods based on the concept of seniority number, defined as the number of singly occupied orbitals in a determinant or an orbital configuration, is proposed and applied to the studies of the potential energy curves (PECs) of H8, N2, and C2 molecules. It is found that the seniority-based VB expansion converges more rapidly toward the full configuration interaction (FCI) or complete active space self-consistent field (CASSCF) limit and produces more accurate PECs with smaller nonparallelity errors than its molecular orbital (MO) theory-based analogue. Test results reveal that the nonorthogonal orbital-based VB theory provides a reverse but more efficient way to truncate the complete active Hilbert space by seniority numbers.

  13. Atoms in Valence Bond. Method, implementation and application

    NARCIS (Netherlands)

    Zielinski, M.L.

    2012-01-01

    The Atoms in Valence Bond (AiVB) approach is presented. The main goal was to develop a new and innovative approach, within the existing Valence Bond framework, to build and analyze the molecular VB wave function in terms of atoms and their atomic states, in a very user-friendly environment. The nece

  14. Novel approach to the concept of bond-valence vectors.

    Science.gov (United States)

    Zachara, Janusz

    2007-11-12

    A new approach to the old idea of deriving a bond-valence vector from the well-known bond-valence concept has been proposed. The foundation of the proposal is the previous electrostatic model in which bond valences are interpreted as electric fluxes. The outcome of this approach is actual vectorial quantities whose magnitudes are strictly but nonlinearly related to the scalar bond valences and are directed along the bond lines. It has been proved that the sum of all these bond-valence vectors drawn from a coordination center to its ligating atoms will be close to zero for the complete coordination sphere. Therefore, unlike the scalar bond valences, the obtained vectors provide information about the spatial arrangement of ligands. The geometrical consequences of the proposed bond-valence vector (BVV) model are analyzed for the geometries of the carbonates, phosphates, and five-coordinated organoaluminum compounds with CO3, PO4, and AlCO4 skeletons, respectively, retrieved from the Cambridge Structural Database. For acyclic carbonates this BVV model allows one to predict the O-C-O angles with a mean absolute error of 1.0 degrees using the empirical C-O distances only. Furthermore, this BVV model is able to quantitatively describe the strains in cyclic carbonates. The preliminary studies for NO2E, PO3E, and SO3E systems with a strongly stereoactive lone electron pair (E) show that the model may serve as a quantitative description of the lone electron pair effect on the coordination sphere. A great advantage of the presented BVV approach is that the derived relation between a bond-valence vector, bond valence, and bond length is given by an uncomplicated equation allowing quick and simple computations, thus providing a new analytical tool for describing the geometry of a coordination sphere that may be applied for structure validation.

  15. Valence bond and von Neumann entanglement entropy in Heisenberg ladders.

    Science.gov (United States)

    Kallin, Ann B; González, Iván; Hastings, Matthew B; Melko, Roger G

    2009-09-11

    We present a direct comparison of the recently proposed valence bond entanglement entropy and the von Neumann entanglement entropy on spin-1/2 Heisenberg systems using quantum Monte Carlo and density-matrix renormalization group simulations. For one-dimensional chains we show that the valence bond entropy can be either less or greater than the von Neumann entropy; hence, it cannot provide a bound on the latter. On ladder geometries, simulations with up to seven legs are sufficient to indicate that the von Neumann entropy in two dimensions obeys an area law, even though the valence bond entanglement entropy has a multiplicative logarithmic correction.

  16. Bond valence parameterslinearly dependent on the molybdenum oxidation states

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on the available crystal data, a linear correlation between R0, the bond valence parameter for a Mo-containing chemical bond, and the Mo oxidation state n was developed for the first time. Using the "universal" value of the parameter B = 0.037 nm, the linear equations of R0-n for Mo-X (X: O, S, N, Cl and F) bonds were established. The oxidation-state independent Mo-O bond valence parameters, R0 = 0.18788 nm and B = 0.03046 nm, published recently have been shown to be a special case of the linearly correlated functions. Some bond valence sum calculations in compounds containing only Mo-O bonds using these para- meters are presented.

  17. Valence-Bond Concepts in Coordination Chemistry and the Nature of Metal-Metal Bonds.

    Science.gov (United States)

    Pauling, Linus; Herman, Zelek S.

    1984-01-01

    Discusses the valence-bond method, applying it to some coordination compounds of metals, especially those involving metal-metal bonds. Suggests that transition metals can form as many as nine covalent bonds, permitting valence-theory to be extended to transition metal compounds in a more effective way than has been possible before. (JN)

  18. Chemical Bonding: The Orthogonal Valence-Bond View

    Directory of Open Access Journals (Sweden)

    Alexander F. Sax

    2015-04-01

    Full Text Available Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO used to construct the wave functions. The transformation of such wave functions into valence bond (VB wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected.

  19. A valence bond study of three-center four-electron pi bonding: electronegativity vs electroneutrality.

    Science.gov (United States)

    DeBlase, Andrew; Licata, Megan; Galbraith, John Morrison

    2008-12-18

    Three-center four-electron (3c4e) pi bonding systems analogous to that of the ozone molecule have been studied using modern valence bond theory. Molecules studied herein consist of combinations of first row atoms C, N, and O with the addition of H atoms where appropriate in order to preserve the 3c4e pi system. Breathing orbital valence bond (BOVB) calculations were preformed at the B3LYP/6-31G**-optimized geometries in order to determine structural weights, pi charge distributions, resonance energies, and pi bond energies. It is found that the most weighted VB structure depends on atomic electronegativity and charge distribution, with electronegativity as the dominant factor. By nature, these systems are delocalized, and therefore, resonance energy is the main contributor to pi bond energies. Molecules with a single dominant VB structure have low resonance energies and therefore low pi bond energies.

  20. 1D valence bond solids in a magnetic field

    Science.gov (United States)

    Iaizzi, Adam; Sandvik, Anders W.

    2015-09-01

    A Valence bond solid (VBS) is a nonmagnetic, long-range ordered state of a quantum spin system where local spin singlets are formed in some regular pattern. We here study the competition between VBS order and a fully polarized ferromagnetic state as function of an external magnetic field in a one-dimensional extended Heisenberg model—the J-Q2 model— using stochastic series expansion (SSE) quantum Monte Carlo simulations with directed loop updates. We discuss the ground state phase diagram.

  1. Mean bond-length variation in crystal structures: a bond-valence approach.

    Science.gov (United States)

    Bosi, Ferdinando

    2014-08-01

    The distortion theorem of the bond-valence theory predicts that the mean bond length 〈D〉 increases with increasing deviation of the individual bond lengths from their mean value according to the equation 〈D〉 = (D' + ΔD), where D' is the length found in a polyhedron having equivalent bonds and ΔD is the bond distortion. For a given atom, D' is expected to be similar from one structure to another, whereas 〈D〉 should vary as a function of ΔD. However, in several crystal structures 〈D〉 significantly varies without any relevant contribution from ΔD. In accordance with bond-valence theory, 〈D〉 variation is described here by a new equation: 〈D〉 = (DRU + ΔDtop + ΔDiso + ΔDaniso + ΔDelec), where DRU is a constant related to the type of cation and coordination environment, ΔDtop is the topological distortion related to the way the atoms are linked, ΔDiso is an isotropic effect of compression (or stretching) in the bonds produced by steric strain and represents the same increase (or decrease) in all the bond lengths in the coordination sphere, ΔDaniso is the distortion produced by compression and stretching of bonds in the same coordination sphere, ΔDelec is the distortion produced by electronic effects. If present, ΔDelec can be combined with ΔDaniso because they lead to the same kind of distortions in line with the distortion theorem. Each D-index, in the new equation, corresponds to an algebraic expression containing experimental and theoretical bond valences. On the basis of this study, the ΔD index defined in bond valence theory is a result of both the bond topology and the distortion theorem (ΔD = ΔDtop + ΔDaniso + ΔDelec), and D' is a result of the compression, or stretching, of bonds (D' = DRU + ΔDiso). The deficiencies present in the bond-valence theory in explaining mean bond-length variations can therefore be overcome, and the observed variations of 〈D〉 in crystal structures can be

  2. Molecular mechanics-valence bond method for planar conjugated hydrocarbon cations.

    Science.gov (United States)

    Hall, Katherine F; Tokmachev, Andrei M; Bearpark, Michael J; Boggio-Pasqua, Martial; Robb, Michael A

    2007-10-07

    We present an extension of the molecular mechanics-valence bond (MMVB) hybrid method to study ground and excited states of planar conjugated hydrocarbon cations. Currently, accurate excited state calculations on these systems are limited to expensive ab initio studies of smaller systems: up to 15 active electrons in 16 pi orbitals with complete active space self-consistent field (CASSCF) theory using high symmetry. The new MMVB extension provides a faster, cheaper treatment to investigate larger cation systems with more than 24 active orbitals. Extension requires both new matrix elements and new parameters: In this paper we present both, for the limited planar case. The scheme is tested for the planar radical cations of benzene, naphthalene, anthracene, and phenanthrene. Calculated MMVB relative energies are in good agreement with CASSCF results for equilibrium geometries on the ground and first excited states, and conical intersections.

  3. A multistate empirical valence bond model for solvation and transport simulations of OH- in aqueous solutions.

    Science.gov (United States)

    Ufimtsev, Ivan S; Kalinichev, Andrey G; Martinez, Todd J; Kirkpatrick, R James

    2009-11-07

    We describe a new multistate empirical valence bond (MS-EVB) model of OH(-) in aqueous solutions. This model is based on the recently proposed "charged ring" parameterization for the intermolecular interaction of hydroxyl ion with water [Ufimtsev, et al., Chem. Phys. Lett., 2007, 442, 128] and is suitable for classical molecular simulations of OH(-) solvation and transport. The model reproduces the hydration structure of OH(-)(aq) in good agreement with experimental data and the results of ab initio molecular dynamics simulations. It also accurately captures the major structural, energetic, and dynamic aspects of the proton transfer processes involving OH(-) (aq). The model predicts an approximately two-fold increase of the OH(-) mobility due to proton exchange reactions.

  4. Empirical valence bond models for reactive potential energy surfaces: a parallel multilevel genetic program approach.

    Science.gov (United States)

    Bellucci, Michael A; Coker, David F

    2011-07-28

    We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent.

  5. Valence-bond quantum Monte Carlo algorithms defined on trees.

    Science.gov (United States)

    Deschner, Andreas; Sørensen, Erik S

    2014-09-01

    We present a class of algorithms for performing valence-bond quantum Monte Carlo of quantum spin models. Valence-bond quantum Monte Carlo is a projective T=0 Monte Carlo method based on sampling of a set of operator strings that can be viewed as forming a treelike structure. The algorithms presented here utilize the notion of a worm that moves up and down this tree and changes the associated operator string. In quite general terms, we derive a set of equations whose solutions correspond to a whole class of algorithms. As specific examples of this class of algorithms, we focus on two cases. The bouncing worm algorithm, for which updates are always accepted by allowing the worm to bounce up and down the tree, and the driven worm algorithm, where a single parameter controls how far up the tree the worm reaches before turning around. The latter algorithm involves only a single bounce where the worm turns from going up the tree to going down. The presence of the control parameter necessitates the introduction of an acceptance probability for the update.

  6. Resonating Valence Bond states for low dimensional S=1 antiferromagnets

    Science.gov (United States)

    Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

    2014-03-01

    We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.

  7. Plaquette valence bond theory of high-temperature superconductivity

    Science.gov (United States)

    Harland, Malte; Katsnelson, Mikhail I.; Lichtenstein, Alexander I.

    2016-09-01

    We present a strong-coupling approach to the theory of high-temperature superconductivity based on the observation of a quantum critical point in the plaquette within the t ,t' Hubbard model. The crossing of ground-state energies in the N =2 -4 sectors occurs for parameters close to the optimal doping. The theory predicts the maximum of the dx2-y2-wave order parameter at the border between localized and itinerant electron behaviors and gives a natural explanation for the pseudogap formation via the soft-fermion mode related to local singlet states of the plaquette in the environment. Our approach follows the general line of resonating valence-bond theory stressing a crucial role of singlets in the physics of high-Tc superconductors but focuses on the formation of local singlets, similar to phenomena observed in frustrated one-dimensional quantum spin models.

  8. Paired-permanent approach to valence bond theory

    Institute of Scientific and Technical Information of China (English)

    吴玮; 吴安安; 莫亦荣; 张乾二

    1996-01-01

    A new function called paired-permanent is defined and widely discussed, and a practicable procedure for evaluations of paired-permanents is proposed, which is similar to the Laplace method for determinants. Using the concept of paired-permanents, an efficient algorithm is presented for evaluating the Hamiltonian and overlap matrix elements in the spin-free form of valence bond (VB) theory. With the new algorithm, a spin-free wavefunction is simply written as a paired-permanent, and an overlap matrix element may be obtained by evaluating a corresponding paired-permanent. Meanwhile, the Hamiltonian matrix element is expressed in terms of the summation of the products of electronic integrals and the corresponding sub-paired-permanents

  9. Modelling of Ion Transport in Solids with a General Bond Valence Based Force-Field

    OpenAIRE

    Adams, S.; R.P. Rao

    2010-01-01

    Empirical bond length - bond valence relations provide insight into the link between structure of and ion transport in solid electrolytes. Building on our earlier systematic adjustment of bond valence (BV) parameters to the bond softness, here we discuss how the squared BV mismatch can be linked to the absolute energy scale and used as a general Morse-type interaction potential for analyzing low-energy pathways in ion conducting solid or mixed conductors either by an energy landscape approach...

  10. Atoms in Valence Bond – AiVB : synopsis and test results

    NARCIS (Netherlands)

    Zielinski, M.L.; van Lenthe, J.H.

    2010-01-01

    The Atoms in Valence Bond (AiVB) method, a new approach in the Valence Bond, is introduced. This approach combines the ideas behind the early Atoms in Molecules (AIM) developments, e.g. by Moffit [21], to understand a molecular wave function in terms of proper atomic wave functions, with the availab

  11. Valence bond phases in S = 1/2 Kane-Mele-Heisenberg model.

    Science.gov (United States)

    Zare, Mohammad H; Mosadeq, Hamid; Shahbazi, Farhad; Jafari, S A

    2014-11-12

    The phase diagram of the Kane-Mele-Heisenberg model in a classical limit [47] contains disordered regions in the coupling space, as the result of competition between different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phases in the quantum limit, for a S = 1/2. Employing exact diagonalization in Sz and nearest neighbour valence bond bases, and bond and plaquette valence bond mean field theories, we show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystals and staggered dimerized phases.

  12. Ab initio calculations of the electronic structure and bonding characteristics of LaB6

    Science.gov (United States)

    Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.

    2005-12-01

    Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.

  13. Ground and excited states of doubly open-shell nuclei from ab initio valence-space Hamiltonians

    CERN Document Server

    Stroberg, S R; Holt, J D; Bogner, S K; Schwenk, A

    2015-01-01

    We present ab initio predictions for ground and excited states of doubly open-shell fluorine and neon isotopes based on chiral two- and three-nucleon interactions. We use the in-medium similarity renormalization group, in both flow-equation and Magnus formulations, to derive mass-dependent sd valence-space Hamiltonians. The experimental ground-state energies are reproduced through neutron number N=14, beyond which a new targeted normal-ordering procedure improves agreement with data and large-scale multi-reference calculations. For spectroscopy, we focus on neutron-rich 23-26F and 24-26Ne isotopes near N=14,16 magic numbers. In all cases we find an agreement with experiment competitive with established phenomenology. Moreover, yrast states are well described in 20Ne and 24Mg, providing an ab initio description of deformation in the medium-mass region.

  14. Ab initio potential energy curves of the valence, Rydberg, and ion-pair states of iodine monochloride, ICl.

    Science.gov (United States)

    Kalemos, Apostolos; Prosmiti, Rita

    2014-09-14

    We present for the first time a coherent ab initio study of 39 states of valence, Rydberg, and ion-pair character of the diatomic interhalogen ICl species through large scale multireference variational methods including spin-orbit effects coupled with quantitative basis sets. Various avoided crossings are responsible for a non-adiabatic behaviour creating a wonderful vista for its theoretical description. Our molecular constants are compared with all available experimental data with the aim to assist experimentalists especially in the high energy regime of up to ~95,000 cm(-1).

  15. A STUDY OF TEMPERATURE-DEPENDENT VALENCE BOND STRUCTURE OF TITANIUM

    Institute of Scientific and Technical Information of China (English)

    X.B. Li; Y.Q. Xie; Y.Z. Nie; H.J. Peng; H.J. Tao; F.X. Yu

    2007-01-01

    On the basis of energy and shape method for the determination of the valence bond (VB) structures of crystal, the valence bond structure of titanium is redetermined at room temperature and calculated in the whole temperature range of 0-1943K. The outer shell electronic distribution of Ti is ec2.9907 .(sc0.4980 + dc2.4927) ef1.0093 in crystal. The temperature dependences of the VB structures of hcp and bcc phases are the same. The VB structures of hcp and bcc phases monotonically increase or decrease with the increase in temperature, but show discontinuous changes at the phase-transformation temperature 1155K.

  16. An Effective Hamiltonian Molecular Orbital-Valence Bond (MOVB) Approach for Chemical Reactions Applied to the Nucleophilic Substitution Reaction of Hydrosulfide Ion and Chloromethane.

    Science.gov (United States)

    Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-01-01

    An effective Hamiltonian mixed molecular orbital and valence bond (EH-MOVB) method is described to obtain an accurate potential energy surface for chemical reactions. Building upon previous results on the construction of diabatic and adiabatic potential surfaces using ab initio MOVB theory, we introduce a diabatic-coupling scaling factor to uniformly scale the ab initio off-diagonal matrix element H(12) such that the computed energy of reaction from the EH-MOVB method is in agreement with the target value. The scaling factor is very close to unity, resulting in minimal alteration of the potential energy surface of the original MOVB model. Furthermore, the relative energy between the reactant and product diabatic states in the EH-MOVB method can be improved to match the experimental energy of reaction. A key ingredient in the EH-MOVB theory is that the off-diagonal matrix elements are functions of all degrees of freedom of the system and the overlap matrix is explicitly evaluated. The EH-MOVB method has been applied to the nucleophilic substitution reaction between hydrosulfide and chloromethane to illustrate the methodology and the results were matched to reproduce the results from ab initio valence bond self-consistent valence bond (VBSCF) calculations. The diabatic coupling (the off-diagonal matrix element in the generalized secular equation) has small variations along the minimum energy reaction path in the EH-MOVB model, whereas it shows a maximum value at the transition state and has nearly zero values in the regions of the ion-dipole complexes from VBSCF calculations. The difference in the diabatic coupling stabilization is attributed to the large overlap integral in the computationally efficient MOVB method.

  17. Size-extensive wave functions for quantum Monte Carlo: A linear scaling generalized valence bond approach

    NARCIS (Netherlands)

    Fracchia, F.; Filippi, C.; Amovilli, C.

    2012-01-01

    We propose a new class of multideterminantal Jastrow–Slater wave functions constructed with localized orbitals and designed to describe complex potential energy surfaces of molecular systems for use in quantum Monte Carlo (QMC). Inspired by the generalized valence bond formalism, we elaborate a coup

  18. Valence bond study on excited states of molecules——Bonding features of the low-lying states of molecule B2

    Institute of Scientific and Technical Information of China (English)

    曹泽星; 吴玮; 张乾二

    1997-01-01

    Based on the correspondence of the molecular orbital theory and valence bond theory to the description of chemical bonds,the ah imtio valence bond (VB) calculations of the low-lying states of diatomic molecules arc realized.The calculation results for the low-lying states of B2 show that the VB calculation has clear-cut physical significance,and its simulation of the behavior of the potential energy surface about the equilibrium position is superior to that of the molecular orbital theory.The valence bond calculation involving only a few bonded tableaus can correctly re fleet the effect of electronic correlation.

  19. A study on configuration-activity relationship of diamminedichloroplatinum (II) by the pseudopotential valence electron-only ab initio calculation method.

    Science.gov (United States)

    Chen, K X; Wu, J A; Ji, R Y

    1987-09-01

    We investigated the cis- and trans-isomers of Pt(NH3)2Cl2 and [Pt(NH3)2]2+ using a quantum chemical non-empirical calculation method, the pseudopotential valence electron-only ab initio method. The electronic structure and electrostatic potential counter maps were in turn determined through the wave functions so obtained. There was a sharp difference between the dipole moments of the cis- and trans-isomers. The electrostatic counter maps of the isomers also had remarkably different features. Based on the interaction between the platinum (II) coordination compound and the base pairs of nucleic acid, the difference in antitumour activity of the isomeric compounds was discussed. It is pointed out that the key factor for antitumour activity is that the platinum (II) coordination compound must be mutually complementary with the target acceptor in both configuration and bonding activity. This mutual-complementary requirement includes a bonding ability of the platinum complex with two negative centers in DNA, so as to form an intrastrand crosslink with two neighbouring guanines.

  20. Valence Virtual Orbitals: An Unambiguous ab Initio Quantification of the LUMO Concept.

    Science.gov (United States)

    Schmidt, Michael W; Hull, Emily A; Windus, Theresa L

    2015-10-15

    Many chemical concepts hinge on the notion of an orbital called the lowest unoccupied molecular orbital, or LUMO. This hypothetical orbital and the much more concrete highest occupied molecular orbital (HOMO) constitute the two "frontier orbitals", which rationalize a great deal of chemistry. A viable LUMO candidate should have a sensible energy value, a realistic shape with amplitude on those atoms where electron attachment or reduction or excitation processes occur, and often an antibonding correspondence to one of the highest occupied MOs. Unfortunately, today's quantum chemistry calculations do not yield useful empty orbitals. Instead, the empty canonical orbitals form a large sea of orbitals, where the interesting valence antibonds are scrambled with the basis set's polarization and diffuse augmentations. The LUMO is thus lost within a continuum associated with a detached electron, as well as many Rydberg excited states. A suitable alternative to the canonical orbitals is proposed, namely, the valence virtual orbitals. VVOs are found by a simple algorithm based on singular value decomposition, which allows for the extraction of all valence-like orbitals from the large empty canonical orbital space. VVOs are found to be nearly independent of the working basis set. The utility of VVOs is demonstrated for construction of qualitative MO diagrams, for prediction of valence excited states, and as starting orbitals for more sophisticated calculations. This suggests that VVOs are a suitable realization of the LUMO, LUMO + 1, ... VVO generation requires no expert knowledge, as the number of VVOs sought is found by counting s-block atoms as having only a valence s orbital, transition metals as having valence s and d, and main group atoms as being valence s and p elements. Closed shell, open shell, or multireference wave functions and elements up to xenon may be used in the present program.

  1. Effects of Magnetic Field on the Valence Bond Property of the Double-Quantum-Dot Molecule

    Institute of Scientific and Technical Information of China (English)

    王立民; 罗莹; 马本堃

    2002-01-01

    The effects of the magnetic field on the valence bond property of the double-quantum-dot molecule are numerically studied by the finite element method and perturbation approach because of the absence of cylindrical symmetry in the horizontally coupled dots. The calculation results show that the energy value of the ground state changes differently from that of the first excited state with increasing magnetic field strength, and they cross under a certain magnetic field. The increasing magnetic field makes the covalent bond state change into an ionic bond state, which agrees qualitatively with experimental results and makes ionic bond states remain. The oscillator strength of transition between covalent bond states decreases distinctly with the increasing magnetic field strength, when the molecule is irradiated by polarized light. Such a phenomenon is possibly useful for actual applications.

  2. Comparison of ion sites and diffusion paths in glasses obtained by molecular dynamics simulations and bond valence analysis

    OpenAIRE

    Muller, Christian; Zienicke, Egbert; Adams, Stefan; Habasaki, Junko; Maass, Philipp

    2006-01-01

    Based on molecular dynamics simulations of a lithium metasilicate glass we study the potential of bond valence sum calculations to identify sites and diffusion pathways of mobile Li ions in a glassy silicate network. We find that the bond valence method is not well suitable to locate the sites, but allows one to estimate the number of sites. Spatial regions of the glass determined as accessible for the Li ions by the bond valence method can capture up to 90% of the diffusion path. These regio...

  3. Nature of the chemical bond and origin of the inverted dipole moment in boron fluoride: a generalized valence bond approach.

    Science.gov (United States)

    Fantuzzi, Felipe; Cardozo, Thiago Messias; Nascimento, Marco Antonio Chaer

    2015-05-28

    The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)Σ(+) and a (3)Π states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that π back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation.

  4. A valence bond model for aqueous Cu(II) and Zn(II) ions in the AMOEBA polarizable force field.

    Science.gov (United States)

    Xiang, Jin Yu; Ponder, Jay W

    2013-04-05

    A general molecular mechanics (MM) model for treating aqueous Cu(2+) and Zn(2+) ions was developed based on valence bond (VB) theory and incorporated into the atomic multipole optimized energetics for biomolecular applications (AMOEBA) polarizable force field. Parameters were obtained by fitting MM energies to that computed by ab initio methods for gas-phase tetra- and hexa-aqua metal complexes. Molecular dynamics (MD) simulations using the proposed AMOEBA-VB model were performed for each transition metal ion in aqueous solution, and solvent coordination was evaluated. Results show that the AMOEBA-VB model generates the correct square-planar geometry for gas-phase tetra-aqua Cu(2+) complex and improves the accuracy of MM model energetics for a number of ligation geometries when compared to quantum mechanical (QM) computations. On the other hand, both AMOEBA and AMOEBA-VB generate results for Zn(2+)-water complexes in good agreement with QM calculations. Analyses of the MD trajectories revealed a six-coordination first solvation shell for both Cu(2+) and Zn(2+) ions in aqueous solution, with ligation geometries falling in the range reported by previous studies. Copyright © 2012 Wiley Periodicals, Inc.

  5. An alternative empirical model for the relationship between the bond valence and the thermal expansion rate of chemical bonds.

    Science.gov (United States)

    Sidey, Vasyl

    2015-08-01

    The relationship between the bond valence s and the thermal expansion rate of chemical bonds (dr/dT) has been closely approximated by using the alternative three-parameter empirical model (dr/dT) = (u + vs)(-1/w), where u, v and w are the refinable parameters. Unlike the s-(dr/dT) model developed by Brown et al. [(1997), Acta Cryst. B53, 750-761], this alternative model can be optimized for particular s-(dr/dT) datasets in the least-squares refinement procedure. For routine calculations of the thermal expansion rates of chemical bonds, the alternative model with the parameters u = -63.9, v = 2581.0 and w = 0.647 can be recommended.

  6. Modelling of Ion Transport in Solids with a General Bond Valence Based Force-Field

    Directory of Open Access Journals (Sweden)

    S. Adams

    2010-12-01

    Full Text Available Empirical bond length - bond valence relations provide insight into the link between structure of and ion transport in solid electrolytes. Building on our earlier systematic adjustment of bond valence (BV parameters to the bond softness, here we discuss how the squared BV mismatch can be linked to the absolute energy scale and used as a general Morse-type interaction potential for analyzing low-energy pathways in ion conducting solid or mixed conductors either by an energy landscape approach or by molecular dynamics (MD simulations. For a wide range of Lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. Our novel BV-based force-field has also been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV-based force-field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials (LiFePO4, LiVPO4F, LiFeSO4F, etc..

  7. A Valence-Bond Nonequilibrium Solvation Model for a Twisting Cyanine Dye

    CERN Document Server

    McConnell, Sean; Olsen, Seth

    2014-01-01

    We study a two-state valence-bond electronic Hamiltonian model of non-equilibrium solvation during the excited-state twisting reaction of monomethine cyanines. These dyes are of interest because of the strong environment-dependent enhancement of their fluorescence quantum yield that results from suppression of competing non-radiative decay via twisted internal charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localization, there are two twisting pathways with different charge localization in the excited state. The Hamiltonian designed to be as simple as possible consistent with a few well-enumerated assumptions. It is defined by three parameters and is a function of two $\\pi$-bond twisting angle coordinates and a single solvation coordinate. For parameters corresponding to symmetric monomethines, there are two low-energy twisting channels on the excited-state surface that lead to a manifold of twisted intramolecular ...

  8. Empirical valence bond model of an SN2 reaction in polar and nonpolar solvents

    Science.gov (United States)

    Benjamin, Ilan

    2008-08-01

    A new model for the substitution nucleophilic reaction (SN2) in solution is described using the empirical valence bond (EVB) method. The model includes a generalization to three dimensions of a collinear gas phase EVB model developed by Mathis et al. [J. Mol. Liq. 61, 81 (1994)] and a parametrization of solute-solvent interactions of four different solvents (water, ethanol, chloroform, and carbon tetrachloride). The model is used to compute (in these four solvents) reaction free energy profiles, reaction and solvent dynamics, a two-dimensional reaction/solvent free energy map, as well as a number of other properties that in the past have mostly been estimated.

  9. A tutorial for understanding chemical reactivity through the valence bond approach.

    Science.gov (United States)

    Usharani, Dandamudi; Lai, Wenzhen; Li, Chunsen; Chen, Hui; Danovich, David; Shaik, Sason

    2014-07-21

    This is a tutorial on the usage of valence bond (VB) diagrams for understanding chemical reactivity in general, and hydrogen atom transfer (HAT) reactivity in particular. The tutorial instructs the reader how to construct the VB diagrams and how to estimate HAT barriers from raw data, starting with the simplest reaction H + H2 and going all the way to HAT in the enzyme cytochrome P450. Other reactions are treated as well, and some unifying principles are outlined. The tutorial projects the unity of reactivity treatments, following Coulson's dictum "give me insight, not numbers", albeit with its modern twist: giving numbers and insight.

  10. Entanglement and SU(n) symmetry in one-dimensional valence bond solid states

    CERN Document Server

    Orus, Roman

    2011-01-01

    Here we evaluate the many-body entanglement properties of a generalized SU(n) valence bond solid state on a chain. Our results follow from a derivation of the transfer matrix of the system which, in combination with symmetry properties, allows for a new, elegant and straightforward evaluation of different entanglement measures. In particular, the geometric entanglement per block, correlation length, von Neumann and R\\'enyi entropies of a block, localizable entanglement and entanglement length are obtained in a very simple way. All our results are in agreement with previous derivations for the SU(2) case.

  11. The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

    Energy Technology Data Exchange (ETDEWEB)

    Domin, D.; Braida, Benoit; Lester Jr., William A.

    2008-05-30

    This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

  12. Photodissociation of carbon dioxide in singlet valence electronic states. I. Six multiply intersecting ab initio potential energy surfaces

    Science.gov (United States)

    Grebenshchikov, Sergy Yu.

    2013-06-01

    The global potential energy surfaces of the first six singlet electronic states of CO2, 1—31A', and 1—31A″ are constructed using high level ab initio calculations. In linear molecule, they correspond to tilde{X}^1Σ _g^+, 11Δu, 1^1Σ _u^-, and 11Πg. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true intersections, both conical and glancing. Near degeneracies can be found for each pair of six states and many intersections involve more than two states. In particular, a fivefold intersection dominates the Franck-Condon zone for the ultraviolet excitation from the ground electronic state. The seam of this intersection traces out a closed loop. All states are diabatized, and a diabatic 5 × 5 potential matrix is constructed, which can be used in quantum mechanical calculations of the absorption spectrum of the five excited singlet valence states.

  13. Valence XPS structure and chemical bond in Cs2UO2Cl4

    Directory of Open Access Journals (Sweden)

    Teterin Yury A.

    2016-01-01

    Full Text Available Quantitative analysis was done of the valence electrons X-ray photoelectron spectra structure in the binding energy (BE range of 0 eV to ~35 eV for crystalline dicaesium tetrachloro-dioxouranium (VI (Cs2UO2Cl4. This compound contains the uranyl group UO2. The BE and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the UO2Cl4(D4h cluster reflecting U close environment in Cs2UO2Cl4 were taken into account. The experimental data show that many-body effects due to the presence of cesium and chlorine contribute to the outer valence (0-~15 eV BE spectral structure much less than to the inner valence (~15 eV-~35 eV BE one. The filled U5f electronic states were theoretically calculated and experimentally confirmed to be present in the valence band of Cs2UO2Cl4. It corroborates the suggestion on the direct participation of the U5f electrons in the chemical bond. Electrons of the U6p atomic orbitals participate in formation of both the inner (IVMO and the outer (OVMO valence molecular orbitals (bands. The filled U6p and the O2s, Cl3s electronic shells were found to make the largest contributions to the IVMO formation. The molecular orbitals composition and the sequence order in the binding energy range 0 eV-~35 eV in the UO2Cl4 cluster were established. The experimental and theoretical data allowed a quantitative molecular orbitals scheme for the UO2Cl4 cluster in the BE range 0-~35 eV, which is fundamental for both understanding the chemical bond nature in Cs2UO2Cl4 and the interpretation of other X-ray spectra of Cs2UO2Cl4. The contributions to the chemical binding for the UO2Cl4 cluster were evaluated to be: the OVMO contribution - 76%, and the IVMO contribution - 24 %.

  14. Conceptual chemistry approach towards the support effect in supported vanadium oxides : Valence bond calculations on the ionicity of vanadium catalysts

    NARCIS (Netherlands)

    Fievez, Tim; De Proft, Frank; Geerlings, Paul; Weckhuysen, Bert M.; Havenith, Remco W. A.

    2011-01-01

    The concept of bond ionicity, obtained via a valence bond analysis, is invoked in the interpretation of the catalytic activity of supported vanadium oxides, in analogy with previous work conducted within the framework of conceptual DFT. For a set of model clusters representing the vanadium oxide sup

  15. Complementary method to locate atomic coordinates by combined searching method of structure-sensitive indexes based on bond valence method

    Institute of Scientific and Technical Information of China (English)

    宋振; 刘小浪; 何丽珠; 夏志国; 刘泉林

    2015-01-01

    Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index (GII) and bond strain index (BSI), are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII&BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions.

  16. Resonant valence bond states in zinc vacancies induce the ferromagnetism of ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Shih-Jye, E-mail: sjs@nuk.edu.tw

    2016-05-06

    A theoretical model was proposed to investigate the mechanism of ferromagnetism in ZnO as well as to simulate the experimental result that the ferromagnetism can be enhanced by UV irradiation as UV photon energy is equivalent to the band gap. In the model, the spin moments arise from the trapped electrons in oxygen vacancy states and coexist with the itinerant electrons which reside in zinc vacancy states and fall into resonant valence bond states. Charge exchange between the conduction band of ZnO and both vacancy states makes electrons on both vacancy states delocalized and results in a decrease of the ferromagnetism as well. - Highlights: • The spin moments of ZnO arise from the electrons trapped in oxygen vacancies. • The itinerant electrons residing in zinc vacancies fall into resonant valence bond states. • The ferromagnetism of ZnO is present as both oxygen and zinc vacancies are coexisting. • The couplings between the conduction band and both vacancy states both make the ferromagnetism decrease.

  17. Z2 gauge theory for valence bond solids on the kagome lattice

    Science.gov (United States)

    Hwang, Kyusung; Huh, Yejin; Kim, Yong Baek

    We present an effective Z2 gauge theory that captures various competing phases in spin-1/2 kagome lattice antiferromagnets: the topological Z2 spin liquid (SL) phase, and the 12-site and 36- site valence bond solid (VBS) phases. Our effective theory is a generalization of the recent Z2 gauge theory proposed for SL phases by Wan and Tchernyshyov. In particular, we investigate possible VBS phases that arise from vison condensations in the SL. In addition to the 12-site and 36-site VBS phases, there exists 6-site VBS that is closely related to the symmetry-breaking valence bond modulation patterns observed in the recent density matrix renormalization group simulations. We find that our results have remarkable consistency with a previous study using a different Z2 gauge theory. Motivated by the lattice geometry in the recently reported vanadium oxyfluoride kagome antiferromagnet, our gauge theory is extended to incorporate lowered symmetry by inequivalent up- and down-triangles. We investigate effects of this anisotropy on the 12-site, 36-site, and 6-site VBS phases. Particularly, interesting dimer melting effects are found in the 36-site VBS. We discuss the implications of our findings and also compare the results with a different type of Z2 gauge theory used in previous studies.

  18. Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the potts model.

    Science.gov (United States)

    Jacobsen, J L; Saleur, H

    2008-02-29

    We determine exactly the probability distribution of the number N_(c) of valence bonds connecting a subsystem of length L>1 to the rest of the system in the ground state of the XXX antiferromagnetic spin chain. This provides, in particular, the asymptotic behavior of the valence-bond entanglement entropy S_(VB)=N_(c)ln2=4ln2/pi(2)lnL disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/3lnL. Our results generalize to the Q-state Potts model.

  19. Valence-bond non-equilibrium solvation model for a twisting monomethine cyanine

    Science.gov (United States)

    McConnell, Sean; McKenzie, Ross H.; Olsen, Seth

    2015-02-01

    We propose and analyze a two-state valence-bond model of non-equilibrium solvation effects on the excited-state twisting reaction of monomethine cyanines. Suppression of this reaction is thought responsible for environment-dependent fluorescence yield enhancement in these dyes. Fluorescence is quenched because twisting is accompanied via the formation of dark twisted intramolecular charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localizations, there are two possible twisting pathways with different charge localizations in the excited state. For parameters corresponding to symmetric monomethines, the model predicts two low-energy twisting channels on the excited-state surface, which leads to a manifold of TICT states. For typical monomethines, twisting on the excited state surface will occur with a small barrier or no barrier. Changes in the solvation configuration can differentially stabilize TICT states in channels corresponding to different bonds, and that the position of a conical intersection between adiabatic states moves in response to solvation to stabilize either one channel or the other. There is a conical intersection seam that grows along the bottom of the excited-state potential with increasing solvent polarity. For monomethine cyanines with modest-sized terminal groups in moderately polar solution, the bottom of the excited-state potential surface is completely spanned by a conical intersection seam.

  20. Valence-bond-solid domain walls in a 2D quantum magnet

    Science.gov (United States)

    Shao, Hui; Guo, Wenan; Sandvik, Anders

    sing quantum Monte Carlo simulations, we study properties of domain walls in a square-lattice S=1/2 Heisenberg model with additional interactions which can drive the system from an antiferromagnetic (AFM) ground state to a valence-bond solid (VBS). We study the finite-size scaling of the domain-wall energy at the putative ''deconfined'' critical AFM-VBS point, which gives access to the critical exponent governing the domain-wall width. This length-scale diverges faster than the correlation length and also is related to the scale of spinon deconfinement. Our results show additional evidence of deconfied quantum criticality and are compatible with critical exponents extracted from finite-size scaling of other quantities. NSFC Grant No. 11175018, NSF Grant No. DMR-1410126.

  1. Resonating Valence Bond Quantum Monte Carlo: Application to the ozone molecule

    CERN Document Server

    Azadi, Sam; Kühne, Thomas D

    2015-01-01

    We study the potential energy surface of the ozone molecule by means of Quantum Monte Carlo simulations based on the resonating valence bond concept. The trial wave function consists of an antisymmetrized geminal power arranged in a single-determinant that is multiplied by a Jastrow correlation factor. Whereas the determinantal part incorporates static correlation effects, the augmented real-space correlation factor accounts for the dynamics electron correlation. The accuracy of this approach is demonstrated by computing the potential energy surface for the ozone molecule in three vibrational states: symmetric, asymmetric and scissoring. We find that the employed wave function provides a detailed description of rather strongly-correlated multi-reference systems, which is in quantitative agreement with experiment.

  2. A new algorithm for inactive orbital optimization in valence bond theory

    Institute of Scientific and Technical Information of China (English)

    CHEN ZhenHua; ZHANG QianEr; WU Wei

    2009-01-01

    This paper presents an efficient algorithm for energy gradients in valence bond self-consistent field (VBSCF) method with non-orthogonal orbitals.The frozen core approximation method is extended to the case of non-orthogonal orbitals.The expressions for the total energy and its gradients are presented by introducing auxiliary orbitals,where inactive orbitals are orthogonal,while active orbitals are non-orthogonal themselves but orthogonal to inactive orbitsls.It is shown that our new algorithm has a low scaling of (N_a+ 1)m~4,where N_a and m are the numbers of the active orbitals and basis functions,respectively,and is more efficient than the existing VBSCF algorithms.

  3. A new algorithm for inactive orbital optimization in valence bond theory

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    This paper presents an efficient algorithm for energy gradients in valence bond self-consistent field(VBSCF) method with non-orthogonal orbitals.The frozen core approximation method is extended to the case of non-orthogonal orbitals.The expressions for the total energy and its gradients are presented by introducing auxiliary orbitals,where inactive orbitals are orthogonal,while active orbitals are non-orthogonal themselves but orthogonal to inactive orbitals.It is shown that our new algorithm has a low scaling of(Na+1)m4,where Na and m are the numbers of the active orbitals and basis functions,respectively,and is more efficient than the existing VBSCF algorithms.

  4. Electric and Magnetic properties Computed for Valence Bond Structures: Is There a Link between Pauling Resonance Energy and Ring Current?

    NARCIS (Netherlands)

    Havenith, R.W.A.

    2006-01-01

    To establish the link between the aromaticity descriptors based on the Pauling resonance energy and the molecular properties, the electric (polarizability) and magnetic (magnetizability) field response properties haven been calculated using the valence bond approach for various molecules and their i

  5. Implications of the complete basis set limit in valence bond theory : a case study of molecular hydrogen

    NARCIS (Netherlands)

    Duke, Brian J.; Havenith, Remco W. A.

    2016-01-01

    The use of larger basis sets to approach the complete basis limit, now common in quantum chemistry, is applied for the first time to a range of valence bond functions for the simplest case of molecular hydrogen. Good convergence of the energy is slow due to difficulty in getting a correct cusp near

  6. Is it True That the Normal Valence-Length Correlation Is Irrelevant for Metal-Metal Bonds?

    Science.gov (United States)

    Singh, Vijay; Dixit, Mudit; Kosa, Monica; Major, Dan Thomas; Levi, Elena; Aurbach, Doron

    2016-04-04

    The most intriguing feature of metal-metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal-metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Hydrogen bond dynamics in liquid water: Ab initio molecular dynamics simulation

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Cheolhee; Kim, Eunae [College of Pharmacy, Chosun University, Gwangju (Korea, Republic of); Yeom, Min Sun [Korea Institute of Science and Technology Information, Daejeon (Korea, Republic of)

    2016-01-15

    The effect of intermolecular interaction on the distribution of the harmonic vibrational frequencies of water molecules was investigated through ab initio molecular dynamics simulations based on the Born-Oppenheimer approach. For single water, the effect of the dynamics of the oxygen atom in single water and the simulation time step on the frequency distribution were examined. The distributions of the OH stretching and HOH bending vibrational frequencies of liquid water were compared to those of single water. The probability distributions of the change in OH bond length and the lifetime of the dangling OH bond were also obtained. The distribution of the frequencies was strongly affected by the long lifetime of the dangling OH bond, resulting in the formation of hydrogen bonds between water molecules.

  8. Probing defects and correlations in the hydrogen-bond network of ab initio water

    CERN Document Server

    Gasparotto, Piero; Ceriotti, Michele

    2016-01-01

    The hydrogen-bond network of water is characterized by the presence of coordination defects relative to the ideal tetrahedral network of ice, whose fluctuations determine the static and time-dependent properties of the liquid. Because of topological constraints, such defects do not come alone, but are highly correlated coming in a plethora of different pairs. Here we discuss in detail such correlations in the case of ab initio water models and show that they have interesting similarities to regular and defective solid phases of water. Although defect correlations involve deviations from idealized tetrahedrality, they can still be regarded as weaker hydrogen bonds that retain a high degree of directionality. We also investigate how the structure and population of coordination defects is affected by approximations to the inter-atomic potential, finding that in most cases, the qualitative features of the hydrogen bond network are remarkably robust.

  9. Nonorthogonal orbital based n-body reduced density matrices and their applications to valence bond theory. III. Second-order perturbation theory using valence bond self-consistent field function as reference.

    Science.gov (United States)

    Chen, Zhenhua; Chen, Xun; Ying, Fuming; Gu, Junjing; Zhang, Huaiyu; Wu, Wei

    2014-10-07

    Using the formulas and techniques developed in Papers I and II of this series, the recently developed second-order perturbation theory based on a valence bond self-consistent field reference function (VBPT2) has been extended by using the internally contracted correction wave function. This ansatz strongly reduces the size of the interaction space compared to the uncontracted wave function and thus improves the capability of the VBPT2 method dramatically. Test calculations show that internally contracted VBPT2 using only a small number of reference valence bond functions, can give results as accuracy as the VBPT2 method and other more sophisticated methods such as full configuration interaction and multireference configuration interaction.

  10. From ab initio quantum chemistry to molecular dynamics: The delicate case of hydrogen bonding in ammonia

    CERN Document Server

    Boese, A D; Martin, J M L; Marx, D; Chandra, Amalendu; Martin, Jan M.L.; Marx, Dominik

    2003-01-01

    The ammonia dimer (NH3)2 has been investigated using high--level ab initio quantum chemistry methods and density functional theory (DFT). The structure and energetics of important isomers is obtained to unprecedented accuracy without resorting to experiment. The global minimum of eclipsed C_s symmetry is characterized by a significantly bent hydrogen bond which deviates from linearity by about 20 degrees. In addition, the so-called cyclic C_{2h} structure is extremely close in energy on an overall flat potential energy surface. It is demonstrated that none of the currently available (GGA, meta--GGA, and hybrid) density functionals satisfactorily describe the structure and relative energies of this nonlinear hydrogen bond. We present a novel density functional, HCTH/407+, designed to describe this sort of hydrogen bond quantitatively on the level of the dimer, contrary to e.g. the widely used BLYP functional. This improved functional is employed in Car-Parrinello ab initio molecular dynamics simulations of liq...

  11. Ab initio parametrization of bond-polarizability model for Raman spectroscopy of complex Si materials

    Science.gov (United States)

    Strubbe, David A.; Grossman, Jeffrey C.

    Classical inter-atomic potentials can be successful at predicting the vibrations of materials at system sizes intractable by quantum methods. However, to predict Raman spectra, electrons must be re-introduced, for example via a bond-polarizability model which attributes the polarizability to cylindrically symmetrical inter-atomic bonds. Parameters in assumed functional forms are fit to experimental spectra, and then a Raman intensity can be computed for each mode. In the case of amorphous silicon, the existing models do not show satisfactory agreement with experimental spectra. To generate a more accurate and transferable bond-polarizability model, we have instead begun with ab initio calculated Raman tensors for a set of a-Si:H structures [DA Strubbe et al., arXiv:1511.01139]. This atomistic data set al.lows us to obtain parameters and functional forms for a general model, without confounding errors from the potentials. This Raman model can be used to study large structural models with relevance for photovoltaics, such as medium- and long-range order in a-Si:H, nanocrystalline Si, amorphous/crystalline interfaces, or a-Si:H nanowires, at sizes that would be inaccessible for ab initio calculations. We analyze the applicability of this approach to other materials systems.

  12. Properties of the random-singlet phase: From the disordered Heisenberg chain to an amorphous valence-bond solid

    Science.gov (United States)

    Shu, Yu-Rong; Yao, Dao-Xin; Ke, Chih-Wei; Lin, Yu-Cheng; Sandvik, Anders W.

    2016-11-01

    We use a strong-disorder renormalization group (SDRG) method and ground-state quantum Monte Carlo (QMC) simulations to study S =1 /2 spin chains with random couplings, calculating disorder-averaged spin and dimer correlations. The QMC simulations demonstrate logarithmic corrections to the power-law decaying correlations obtained with the SDRG scheme. The same asymptotic forms apply both for systems with standard Heisenberg exchange and for certain multispin couplings leading to spontaneous dimerization in the clean system. We show that the logarithmic corrections arise in the valence-bond (singlet pair) basis from a contribution that cannot be generated by the SDRG scheme. In the model with multispin couplings, where the clean system dimerizes spontaneously, random singlets form between spinons localized at domain walls in the presence of disorder. This amorphous valence-bond solid is asymptotically a random-singlet state and only differs from the random-exchange Heisenberg chain in its short-distance properties.

  13. Absence of superconductivity and valence bond order in the Hubbard-Heisenberg model for organic charge-transfer solids.

    Science.gov (United States)

    Gomes, N; Clay, R T; Mazumdar, S

    2013-09-25

    A frustrated, effective ½-filled band Hubbard-Heisenberg model has been proposed for describing the strongly dimerized charge-transfer solid families κ-(ET)2X and Z[Pd(dmit)2]2. In addition to showing unconventional superconductivity, these materials also exhibit antiferromagnetism, candidate spin-liquid phases, and, in the case of Z=EtMe3P, a spin-gapped phase that has sometimes been referred to as a valence bond solid. We show that neither superconductivity nor the valence bond order phase occurs within the Hubbard-Heisenberg model. We suggest that a description based on ¼-filling, that is reached when the carrier concentration per molecule instead of per dimer is considered, thus may be appropriate.

  14. Kekulé-based Valence Bond Model.Ⅱ. Diels-Alder Reactivity of Polycyclic Aromatic Hydrocarbons

    Institute of Scientific and Technical Information of China (English)

    MA,Jing(马晶); LI,Shu-Hua(黎书华); JIANG,Yuan-Sheng(江元生)

    2002-01-01

    The Kekule-based valence bond ( VB ) method was employed to study the ground state properties of 52 polycyclic aromatic hydrocarbons. The reactivity indices defined upon our VB calculations were demonstrated to be capable of quantitatively interpreting the secnd order rate constants of the Diels-Alder reactions. The qualitative trends of the reactivities of many homologous series can be also explained based on the local aromaticity index defined in this work.

  15. Theoretical description of electronically excited vinylidene up to 10 eV: First high level ab initio study of singlet valence and Rydberg states

    Energy Technology Data Exchange (ETDEWEB)

    Boyé-Péronne, Séverine; Gauyacq, Dolores [Institut des Sciences Moléculaires d’Orsay, UMR 8214, CNRS and Université Paris-Sud, Bât. 210, F-91405 Orsay Cedex (France); Liévin, Jacques, E-mail: jlievin@ulb.ac.be [Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, Cpi 160/09, 50 Av. F.D. Roosevelt, B-1050 Bruxelles (Belgium)

    2014-11-07

    The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0–10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores {sup 2}A{sub 1} and {sup 2}B{sub 1} results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the {sup 2}B{sub 1} cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the {sup 2}A{sub 1} ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic

  16. Application of the bond valence method in the non-isovalent semiconductor alloy (GaN)1-x(ZnO)x

    Science.gov (United States)

    Liu, Jian

    2016-10-01

    This paper studies the bond valence method (BVM) and its application in the non-isovalent semiconductor alloy (GaN)1-x(ZnO)x. Particular attention is paid to the role of short-range order (SRO). The theoretical standing of the BVM is examined by density-functional theory (DFT) calculations. Combining the BVM with Monte-Carlo simulations and a DFT-based cluster expansion model, bond-length distributions and bond-angle variations are predicted. The connection between bond valence and bond stiffness is also discussed. Finally the BVM is extended to the modelling of an interatomic potential.

  17. Intramolecular hydrogen bond: Can it be part of the basis set of valence internal coordinates in normal mode analysis?

    Indian Academy of Sciences (India)

    Sarvesh Kumar Pandey; Prasanta Das; Puspendu K Das; Elangannan Arunan; Sadasivam Manogaran

    2015-06-01

    It has been shown earlier1 that the relaxed force constants (RFCs) could be used as a measure of bond strength only when the bonds form a part of the complete valence internal coordinates (VIC) basis. However, if the bond is not a part of the complete VIC basis, its RFC is not necessarily a measure of bond strength. Sometimes, it is possible to have a complete VIC basis that does not contain the intramolecular hydrogen bond (IMHB) as part of the basis. This means the RFC of IMHB is not necessarily a measure of bond strength. However, we know that IMHB is a weak bond and hence its RFC has to be a measure of bond strength. We resolve this problem of IMHB not being part of the complete basis by postulating `equivalent’ basis sets where IMHB is part of the basis at least in one of the equivalent sets of VIC. As long as a given IMHB appears in one of the equivalent complete VIC basis sets, its RFC could be used as a measure of bond strength parameter.

  18. The Nature of the Idealized Triple Bonds Between Principal Elements and the σ Origins of Trans-Bent Geometries-A Valence Bond Study.

    Science.gov (United States)

    Ploshnik, Elina; Danovich, David; Hiberty, Philippe C; Shaik, Sason

    2011-04-12

    We describe herein a valence bond (VB) study of 27 triply bonded molecules of the general type X≡Y, where X and Y are main element atoms/fragments from groups 13-15 in the periodic table. The following conclusions were derived from the computational data: (a) Single π-bond and double π-bond energies for the entire set correlate with the "molecular electronegativity", which is the sum of the X and Y electronegativites for X≡Y. The correlation with the molecular electronegativity establishes a simple rule of periodicity: π-bonding strength generally increases from left to right in a period and decreases down a column in the periodic table. (b) The σ frame invariably prefers trans bending, while π-bonding gets destabilized and opposes the trans distortion. In HC≡CH, the π-bonding destabilization overrides the propensity of the σ frame to distort, while in the higher row molecules, the σ frame wins out and establishes trans-bent molecules with 2(1)/2 bonds, in accord with recent experimental evidence based on solid state (29)Si NMR of the Sekiguchi compound. Thus, in the trans-bent molecules "less bonds pay more". (c) All of the π bonds show significant bonding contributions from the resonance energy due to covalent-ionic mixing. This quantity is shown to correlate linearly with the corresponding "molecular electronegativity" and to reflect the mechanism required to satisfy the equilibrium condition for the bond. The π bonds for molecules possessing high molecular electronegativity are charge-shift bonds, wherein bonding is dominated by the resonance energy of the covalent and ionic forms, rather than by either form by itself.

  19. Nuclear quantum effect on intramolecular hydrogen bond of hydrogen maleate anion: An ab initio path integral molecular dynamics study

    Science.gov (United States)

    Kawashima, Yukio; Tachikawa, Masanori

    2013-05-01

    Ab initio path integral molecular dynamics simulation was performed to understand the nuclear quantum effect on the hydrogen bond of hydrogen malonate anion. Static calculation predicted the proton transfer barrier as 0.12 kcal/mol. Conventional ab initio molecular dynamics simulation at 300 K found proton distribution with a double peak on the proton transfer coordinate. Inclusion of thermal effect alone elongates the hydrogen bond length, which increases the barrier height. Inclusion of nuclear quantum effect washes out this barrier, and distributes a single broad peak in the center. H/D isotope effect on the proton transfer is also discussed.

  20. Delocalized mixed-valence bi- and trinuclear complexes with short Cu-Cu bonds.

    Science.gov (United States)

    Yang, Lei; Powell, Douglas R; Klein, Eric L; Grohmann, Andreas; Houser, Robert P

    2007-08-20

    Two mixed-valence copper complexes were synthesized with ligands N-(2-pyridylmethyl)acetamide (Hpmac) and N,N'-(2-methyl-2-pyridylpropan-1,3-diyl)bis(acetamide) (H2pp(ac)2). Dimer [Cu2(pmac)2]OTf and trimer [Cu3(pp(ac)2)2].NaOTf both contain fully delocalized, mixed-valence Cu(1.5)Cu(1.5) moieties.

  1. A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

    DEFF Research Database (Denmark)

    Holland, D.M.P.; Shaw, D.A.; Stener, Mauro

    2016-01-01

    absorption bands due to excitation from the 1e00 or 6e0 orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled...

  2. Electronic structure and bond length dependence of the effective valence shell Hamiltonian of S2 as studied by quasidegenerate many-body perturbation theory

    Science.gov (United States)

    Wang, Xiao-Chuan; Freed, Karl F.

    1987-03-01

    The effective valence shell Hamiltonian (Hv) of S2 is calculated as a function of internuclear distance using quasidegenerate many-body perturbation theory with the full valence space spanned by eight valence orbitals. Calculated potential curves and excitation energies for several valence states are in good agreement with experiment and are compared with configuration interaction calculations using the same primitive basis. In order to test assumptions of semiempirical theories, we also perform a more approximate calculation of Hv in which the valence space is constructed as the union of the atomic valence spaces with the atomic orbitals taken from atomic SCF calculations. A new and important feature of this approximate, correlated Hv is the use of optimized valence and excited orbitals as determined from a constrained SCF procedure. The matrix elements of this approximate, correlated Hv are transformed to the original nonorthogonal atomic valence basis, and their bond length dependences are fit with simple analytical functions. Some calculated Hv matrix elements agree with the forms commonly postulated for semiempirical integrals, while others display quite different behavior. An example of the latter are the one-center, two-electron integrals which depend significantly on bond length in marked contrast to semiempirical theories which assume them to be bond length independent.

  3. Electric and magnetic properties computed for valence bond structures: is there a link between pauling resonance energy and ring current?

    Science.gov (United States)

    Havenith, Remco W A

    2006-04-28

    To establish the link between the aromaticity descriptors based on the Pauling resonance energy and the molecular properties, the electric (polarizability) and magnetic (magnetizability) field response properties have been calculated using the valence bond approach for various molecules and their individual Kekulé resonance structures. The results show that there is no direct relationship between the Pauling resonance energy and the properties; the response properties are weighted averages of the properties of the individual structures. According to the aromaticity criteria based on molecular properties, one-structure benzene would be aromatic; thus, concerning molecular properties, spin-coupled bonds do not behave like localized bonds in Lewis structures, with which they are usually associated.

  4. Electrostatically enhanced FF interactions through hydrogen bonding, halogen bonding and metal coordination: an ab initio study.

    Science.gov (United States)

    Bauzá, Antonio; Frontera, Antonio

    2016-07-27

    In this manuscript the ability of hydrogen and halogen bonding interactions, as well as metal coordination to enhance FF interactions involving fluorine substituted aromatic rings has been studied at the RI-MP2/def2-TZVPD level of theory. We have used 4-fluoropyridine, 4-fluorobenzonitrile, 3-(4-fluorophenyl)propiolonitrile and their respective meta derivatives as aromatic compounds. In addition, we have used HF and IF as hydrogen and halogen bond donors, respectively, and Ag(i) as the coordination metal. Furthermore, we have also used HF as an electron rich fluorine donor entity, thus establishing FF interactions with the above mentioned aromatic systems. Moreover, a CSD (Cambridge Structural Database) search has been carried out and some interesting examples have been found, highlighting the impact of FF interactions involving aromatic fluorine atoms in solid state chemistry. Finally, cooperativity effects between FF interactions and both hydrogen and halogen bonding interactions have been analyzed and compared. We have also used Bader's theory of "atoms in molecules" to further describe the cooperative effects.

  5. Using Raman Spectroscopy and ab initio Calculations to Investigate lntermolecular Hydrogen Bonds in Binary Mixture (Tetrahydrofuran+Water)

    Institute of Scientific and Technical Information of China (English)

    WU Nan-nan; OUYANG Shun-li; LI Zuo-wei; LIU Jing-yao; GAO Shu-qin

    2011-01-01

    We analyzed the properties and structures of the hydrogen-bonded complexes of tetrahydrofuran(THF)and water by means of experimental Raman spectra and ab initio calculations.The optimized geometries and vibrational frequencies of the neat THF molecule and its hydrogen-bonded complexes with water(THF/H2O) were calculated at the MP2/6-31 l+G(d,p) level of theory.We found that the intermolecular hydrogen bonds which are formed from the binary mixtures of the neat THF and water with different molar ratios could explain the changes in wavenumber position and linewidth very well.The combination of ab initio calculations and experimental Raman spectral data provides an insight into the hydrogen bonds leading to the concentration dependent changes in the spectral features.

  6. Structural, dynamical, electronic, and bonding properties of laser-heated silicon: An ab initio molecular-dynamics study

    NARCIS (Netherlands)

    Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.

    1997-01-01

    The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to simulate laser heating of crystalline silicon. We found that a high concentration of excited electrons dramatically weakens the covalent bonding. As a result the system undergoes a melting t

  7. Valence electron structure and bonding features of RuB2 and OSB2: The empirical electron theory calculations

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The valence electron structure (VES) of RuB2 and OsB2 were calculated by the empirical electron theory (EET) of solids and molecules and compared with the results derived from the first-principles calculations. The distributions of covalent electrons in different bonds indicate that B-B and B-Me have remarkably covalent bonding characters. Lattice electrons cruising around Me-Me layers are found to have great influences on electronic conductivity and high temperature plasticity. The ultra-high values of elastic constant Cn in the two compounds originate from close-packed covalent bonding along the c axis. Uneven bond strengths and distributions of covalent bonds, especially for B-Afe bonds, yield significant anisotropy. Low ratios of lattice electrons to covalent electrons suggest the intrinsic embrittlement in crystals. The fact that the calculated cohesive energies well agree with experimental results demonstrates the good suitability of the EET calculations in estimating cohesive energy for transition-metal borides.

  8. Photochemistry of hydrogen bonded heterocycles probed by photodissociation experiments and ab initio methods.

    Science.gov (United States)

    Slavíček, Petr; Fárník, Michal

    2011-07-14

    In this perspective article, we focus on the photochemistry of five-membered nitrogen containing heterocycles (pyrrole, imidazole and pyrazole) in clusters. These heterocycles represent paradigmatic structures for larger biologically active heterocyclic molecules and complexes. The dimers of the three molecules are also archetypes of different bonding patterns: N-H···π interaction, N-H···N hydrogen bond and double hydrogen bond. We briefly review available data on photochemistry of the title molecules in the gas phase, but primarily we focus on the new reaction channels opened upon the complexation with other heterocycles or solvent molecules. Based on ab initio calculations we discuss various possible reactions in the excited states of the clusters: (1) hydrogen dissociation, (2) hydrogen transfer between the heterocyclic units, (3) molecular ring distortion, and (4) coupled electron-proton transfer. The increasing photostability with complexity of the system can be inferred from experiments with photodissociation in these clusters. A unified view on photoinduced processes in five-membered N-heterocycles is provided. We show that even though different deactivation channels are energetically possible for the complexed heterocycles, in most cases the major result is a fast reconstruction of the ground state. The complexed or solvated heterocycles are thus inherently photostable although the stability can in principle be achieved via different reaction routes.

  9. An Ab Initio MP2 Study of HCN-HX Hydrogen Bonded Complexes

    Directory of Open Access Journals (Sweden)

    Araújo Regiane C.M.U.

    1998-01-01

    Full Text Available An ab initio MP2/6-311++G** study has been performed to obtain geometries, binding energies and vibrational properties of HCN-HX H-bonded complexes with X = F, Cl, NC, CN and CCH. These MP2/6-311++G** results have revealed that: (i the calculated H-bond lengths are in very good agreement with the experimental ones; (ii the H-bond strength is associated with the intermolecular charge transfer and follows the order: HCN-HNC ~ HCN-HF > HCN-HCl ~ HCN-HCN > HCN-HCCH; (iii BSSE correction introduces an average reduction of 2.4 kJ/mol on the MP2/6-311++G** binding energies, i.e. 11% of the uncorrected binding energy; (iv the calculated zero-point energies reduce the stability of these complexes and show a good agreement with the available experimental values; (v the H-X stretching frequency is shifted downward upon H-bond formation. This displacement is associated with the H-bond length; (vi The more pronounced effect on the infrared intensities occurs with the H-X stretching intensity. It is much enhanced after complexation due to the charge-flux term; (vii the calculated intermolecular stretching frequencies are in very good agreement with the experimental ones; and, finally, (viii the results obtained for the HCN-HX complexes follow the same profile as those found for the acetylene-HX series but, in the latter case, the effects on the properties of the free molecules due to complexation are less pronounced than those in HCN-HX.

  10. Photodissociation of carbon dioxide in singlet valence electronic states. I. Six multiply intersecting ab initio potential energy surfaces

    OpenAIRE

    Grebenshchikov, Sergy Yu.

    2013-01-01

    The global potential energy surfaces of the first six singlet electronic states of CO$_2$, 1---3$^1/!A'$ and 1---3$^1/!A"$ are constructed using high level ab initio calculations. In linear molecule, they correspond to $\\tilde{X}^1\\Sigma_g^+$, $1^1\\Delta_u$, $1^1\\Sigma_u^-$, and $1^1\\Pi_g$. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true int...

  11. Kekulé-based Valence Bond Model.I. The Ground-state Properties of Conjugated π-Systems

    Institute of Scientific and Technical Information of China (English)

    LI,Shu-Hua(黎书华); MA,Jing(马晶); JIANG,Yuan-Sheng(江元生)

    2002-01-01

    The Kekulé-based valence bond ( VB ) method, in which the VB model is solved using covalent Kekulé structures as basis functions, is justified in the present work. This method is dimonstrated to provide satisfactory descriptions for resoance energies and bond ang lengths of benzenoid hydrocarbons, being in good agreement with SCF-MO and experimental results. In additicn, an alternative way of discyssing characters of localizedsubstructures within a polyclic benzenoid system is suggested based upon such sunokufied VB calculations. Finally,the symmetries of VB ground states for nonalternant conjugated systems are also illustrated to be obtainable through these calculations, presenting very useful information for understanding the chemical behaviors of some nonalternant conjugated molecules.

  12. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    Science.gov (United States)

    Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

    2016-05-05

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  13. Complex Magnetism of Lanthanide Intermetallics and the Role of their Valence Electrons: Ab Initio Theory and Experiment.

    Science.gov (United States)

    Petit, L; Paudyal, D; Mudryk, Y; Gschneidner, K A; Pecharsky, V K; Lüders, M; Szotek, Z; Banerjee, R; Staunton, J B

    2015-11-13

    We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab initio electronic structure theory which includes disordered local moments and strong f-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with a pressure of +1.5 K kbar(-1) for GdCd confirmed by our experimental measurements of +1.6  K kbar(-1). Moreover, we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by noncollinear, canted magnetic order at low temperatures. Replacing 35% of the Mg atoms with Zn removes this transition, in excellent agreement with long-standing experimental data.

  14. Ab initio path-integral molecular dynamics and the quantum nature of hydrogen bonds

    Science.gov (United States)

    Yexin, Feng; Ji, Chen; Xin-Zheng, Li; Enge, Wang

    2016-01-01

    The hydrogen bond (HB) is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects (NQEs) on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice. Project supported by the National Natural Science Foundation of China (Grant Nos. 11275008, 91021007, and 10974012) and the China Postdoctoral Science Foundation (Grant No. 2014M550005).

  15. Hydrogen-hydrogen bonds in highly branched alkanes and in alkane complexes: A DFT, ab initio, QTAIM, and ELF study.

    Science.gov (United States)

    Monteiro, Norberto K V; Firme, Caio L

    2014-03-06

    The hydrogen-hydrogen (H-H) bond or hydrogen-hydrogen bonding is formed by the interaction between a pair of identical or similar hydrogen atoms that are close to electrical neutrality and it yields a stabilizing contribution to the overall molecular energy. This work provides new, important information regarding hydrogen-hydrogen bonds. We report that stability of alkane complexes and boiling point of alkanes are directly related to H-H bond, which means that intermolecular interactions between alkane chains are directional H-H bond, not nondirectional induced dipole-induced dipole. Moreover, we show the existence of intramolecular H-H bonds in highly branched alkanes playing a secondary role in their increased stabilities in comparison with linear or less branched isomers. These results were accomplished by different approaches: density functional theory (DFT), ab initio, quantum theory of atoms in molecules (QTAIM), and electron localization function (ELF).

  16. Why Static O-H Bond Parameters Cannot Characterize the Free Radical Scavenging Activity of Phenolic Antioxidants: ab initio Study

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The static O-H bond parameters including O-H bond length, O-H charge difference, O-H Mulliken population and O-H bond stretching force constant (k) for 17 phenols were calculated by ab initio method HF/6-31G**. In combination with the O-H bond dissociation enthalpies (BDE) of the phenols determined by experiment, it was found that there were poor correlationships between the static O-H bond parameters and O-H BDE. Considering the good correlationship between O-H BDE and logarithm of free radical scavenging rate constant for phenolic antioxidant, it is reasonable to believe that the ineffectiveness of static O-H bond parameters in characterizing antioxidant activity arises from the fact that they cannot measure the O-H BDE.

  17. Photodissociation of carbon dioxide in singlet valence electronic states. I. Six multiply intersecting ab initio potential energy surfaces

    CERN Document Server

    Grebenshchikov, Sergy Yu

    2013-01-01

    The global potential energy surfaces of the first six singlet electronic states of CO$_2$, 1---3$^1/!A'$ and 1---3$^1/!A"$ are constructed using high level ab initio calculations. In linear molecule, they correspond to $\\tilde{X}^1\\Sigma_g^+$, $1^1\\Delta_u$, $1^1\\Sigma_u^-$, and $1^1\\Pi_g$. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true intersections, both conical and glancing. Near degeneracies can be found for each pair of six states and many intersections involve more than two states. In particular, a fivefold intersection dominates the Franck-Condon zone for the ultraviolet excitation from the ground electronic state. The seam of this intersection traces out a closed loop. All states are diabatized, and a diabatic $5\\times 5$ potential matrix is constructed, which can be used in quantum mechanical calculations of the absorption spectrum of the five exci...

  18. Phosphorous bonding in PCl3:H2O adducts: A matrix isolation infrared and ab initio computational studies

    Science.gov (United States)

    Joshi, Prasad Ramesh; Ramanathan, N.; Sundararajan, K.; Sankaran, K.

    2017-01-01

    Non-covalent interaction between PCl3 and H2O was studied using matrix isolation infrared spectroscopy and ab initio computations. Computations indicated that the adducts are stabilized through novel P⋯O type phosphorus bonding and conventional Psbnd Cl⋯H type hydrogen bonding interactions, where the former adduct is the global minimum. Experimentally, the P⋯O phosphorus bonded adduct was identified in N2 matrix, which was evidenced from the shifts in the vibrational wavenumbers of the modes involving PCl3 and H2O sub-molecules. Atoms in Molecules and Natural Bond Orbital analyses have been performed to understand the nature of interactions in the phosphorus and hydrogen bonded adducts. Interestingly, experimental evidence for the formation of higher PCl3sbnd H2O adduct was also observed in N2 matrix.

  19. Ab initio path integral molecular dynamics simulation study on the dihydrogen bond of NH4+⋯BeH2

    Science.gov (United States)

    Hayashi, Aiko; Shiga, Motoyuki; Tachikawa, Masanori

    2005-07-01

    An ab initio path integral molecular dynamics simulation has been performed to study the quantum and thermal effects of a dihydrogen bonded cation, NH4+⋯BeH2. In this system, an attractive interaction exists between two neighboring hydrogen atoms as N δ- H δ+ ⋯H δ- Be δ+ involving large-amplitude of vibration. Some properties playing a key role for this dihydrogen bonded system, such as the bond length, bond angle, and distribution of atomic charges, are investigated in detail by comparing the results of path integral and classical molecular dynamics with those of the equilibrium structure. It was found that the atomic charges of H δ+ and H δ- are decreased and the dihydrogen H δ+ ⋯H δ- bond length is expanded as the thermal and zero-point quantum effects.

  20. Solvent-induced red-shifts for the proton stretch vibrational frequency in a hydrogen-bonded complex. 1. A valence bond-based theoretical approach.

    Science.gov (United States)

    Kiefer, Philip M; Pines, Ehud; Pines, Dina; Hynes, James T

    2014-07-17

    A theory is presented for the proton stretch vibrational frequency νAH for hydrogen (H-) bonded complexes of the acid dissociation type, that is, AH···B ⇔ A(-)···HB(+)(but without complete proton transfer), in both polar and nonpolar solvents, with special attention given to the variation of νAH with the solvent's dielectric constant ε. The theory involves a valence bond (VB) model for the complex's electronic structure, quantization of the complex's proton and H-bond motions, and a solvent coordinate accounting for nonequilibrium solvation. A general prediction is that νAH decreases with increasing ε largely due to increased solvent stabilization of the ionic VB structure A(-)···HB(+) relative to the neutral VB structure AH···B. Theoretical νAH versus 1/ε slope expressions are derived; these differ for polar and nonpolar solvents and allow analysis of the solvent dependence of νAH. The theory predicts that both polar and nonpolar slopes are determined by (i) a structure factor reflecting the complex's size/geometry, (ii) the complex's dipole moment in the ground vibrational state, and (iii) the dipole moment change in the transition, which especially reflects charge transfer and the solution phase proton potential shapes. The experimental proton frequency solvent dependence for several OH···O H-bonded complexes is successfully accounted for and analyzed with the theory.

  1. Mott insulator to high Tc superconductor via pressure: resonating valence bond theory and prediction of new systems.

    Science.gov (United States)

    Baskaran, G

    2003-05-16

    Mott insulator superconductor transition, via pressure and no external doping, is studied in orbitally nondegenerate spin-1 / 2 systems. It is presented as another resonating valence bond route to high T(c) superconductivity. We propose a "strong coupling" hypothesis that views long range Coulomb force driven first order Mott transition as a self-doping process that also preserves superexchange on the metal side. We present a two-species t-J model where conserved N0 doubly occupied (e(-)) sites and N0 empty sites (e(+)) hop in the background of N-2N(0) singly occupied (neutral) sites in a lattice of N sites. An equivalence to the regular t-J model is made. Some old and new systems are predicted to be candidates for pressure-induced high T(c) superconductivity.

  2. On the efficiency of VBSCF algorithms, a comment on "An efficient algorithm for energy gradients and orbital optimization in valence bond theory"

    NARCIS (Netherlands)

    van Lenthe, J. H.; Broer-Braam, H. B.; Rashid, Z.

    2012-01-01

    We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an algori

  3. Communication: ab initio simulations of hydrogen-bonded ferroelectrics: collective tunneling and the origin of geometrical isotope effects.

    Science.gov (United States)

    Wikfeldt, K T; Michaelides, A

    2014-01-28

    Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains - facilitated by quantum mechanical tunneling - is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.

  4. Two states are not enough: quantitative evaluation of the valence-bond intramolecular charge-transfer model and its use in predicting bond length alternation effects.

    Science.gov (United States)

    Jarowski, Peter D; Mo, Yirong

    2014-12-15

    The structural weights of the canonical resonance contributors used in the Two-state valence-bond charge-transfer model, neutral (N, R1) and ionic (VB-CT, R2), to the ground states and excited states of a series of linear dipolar intramolecular charge-transfer chromophores containing a buta-1,3-dien-1,4-diyl bridge have been computed by using the block-localized wavefunction (BLW) method at the B3LYP/6-311+G(d) level to provide the first quantitative assessment of this simple model. Ground- and excited-state analysis reveals surprisingly low ground-state structural weights for the VB-CT resonance form using either this Two-state model or an expanded Ten-state model. The VB-CT state is found to be more prominent in the excited state. Individual resonance forms were structurally optimized to understand the origins of the bond length alternation (BLA) of the bridging unit. Using a Wheland energy-based weighting scheme, the weighted average of the optimized bond lengths with the Two-state model was unable to reproduce the BLA features with values 0.04 to 0.02 Å too large compared to the fully delocalized (FD) structure (BLW: ca. -0.13 to -0.07 Å, FD: ca. -0.09 to -0.05 Å). Instead, an expanded Ten-state model fit the BLA values of the FD structure to within only 0.001 Å of FD. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. A Valence Bond Description of the Prefulvene Extended Conical Intersection Seam of Benzene.

    Science.gov (United States)

    Blancafort, Lluís; Robb, Michael A

    2012-12-11

    The permutational isomers of the prefulvene-like minimum energy conical intersection lie on an extended conical intersection seam, where they are connected by higher symmetry structures. Here, we present a VB analysis of the electronic states involved along this extended seam. The VB method produces a spin-exchange density (ie. a bonding pattern) that provides the basis to assign resonance structures to the states. The results show that in the high symmetry region of the seam, the character of the states is dominated by the positive and negative combination of the Kekulé structures, (A+B) and (A-B). The low energy parts of the seam, comprised of lower symmetry conical intersection structures, are stabilized by mixing with the Dewar resonance structures. This feature is responsible for the stability of the benzvalene-like conical intersections. The validity of the VB model is confirmed by calculating the branching space vectors at this level of theory, which are in good agreement with the CASSCF calculated vectors. The VB analysis has also allowed us to complete our picture of the global seam, since it has provided the clue to locate a conical intersection saddle point that interconverts two minima of the prefulvene conical intersection where the carbon bent out of the plane is inverted and rotated by 60°. This saddle point has a benzvalene-like geometry, in agreement with the VB picture.

  6. New Variational Method for the Ab Initio Study in Valence Coordinates of the Renner-Teller Effect in Tetra-Atomic Systems.

    Science.gov (United States)

    Jutier, Laurent; Léonard, Céline

    2010-05-11

    A new variational methodology for the treatment of the Renner-Teller effect in tetra-atomic molecules has been developed in valence coordinates. The kinetic-energy operator of Bramley et al. [Mol. Phys. 1991, 73, 1183] for any sequentially bonded four-atom molecule, A-B-C-D, in the singlet nondegenerate electronic state has been adapted to the Renner-Teller and spin couplings by modifying the expression of the nuclear angular momentum. The total Schrödinger equation is solved by diagonalizing the Hamiltonian matrix in a three-step contraction scheme. The main advantage of this new theoretical development is the possibility of studying different isotopomers using the same potential-energy surfaces. This procedure has been tested on HCCH(+) and its deuterated derivatives DCCD(+) and DCCH(+). The calculated rovibronic band origins were compared with previous data deduced from the Jacobi coordinates methodology, dimensionality reduced variational treatment, and photoelectron spectra with a good global agreement. Rotational structures for these systems are also tackled.

  7. A bottom-up valence bond derivation of excitation energies in 1D-like delocalized systems.

    Science.gov (United States)

    Kepenekian, Mikaël; Robert, Vincent; Boilleau, Corentin; Malrieu, Jean-Paul

    2012-01-28

    Using the chemically relevant parameters hopping integral t(0) and on-site repulsion energy U, the charge gap (lowest dipolarly allowed transition energy) in 1D systems is examined through a bottom-up strategy. The method is based on the locally ionized states, the energies of which are corrected using short-range delocalization effects. In a valence bond framework, these states interact to produce an excitonic matrix which accounts for the delocalized character of excited states. The treatment, which gives access to the correlated spectrum of ionization potentials, is entirely analytical and valid whatever the U/|t(0)| ratio for such systems ruled by Peierls-Hubbard Hamiltonians. This second-order analytical derivation is finally confronted to numerical results of a renormalized excitonic treatment using larger blocks as functions of the U/|t(0)| ratio. The method is applied to dimerized chains and to fused polybenzenic 1D lattices. Such approaches complement the traditional Bloch-function based picture and deliver a conceptual understanding of the charge gap opening process based on a chemical intuitive picture.

  8. Reactive force field simulation of proton diffusion in BaZrO{sub 3} using an empirical valence bond approach

    Energy Technology Data Exchange (ETDEWEB)

    Raiteri, Paolo; Gale, Julian D [Nanochemistry Research Institute, Department of Chemistry, Curtin University, GPO Box 1987, Perth, WA 6845 (Australia); Bussi, Giovanni, E-mail: paolo@ivec.org, E-mail: julian@ivec.org [Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, 34136 Trieste (Italy)

    2011-08-24

    A new reactive force field to describe proton diffusion within the solid oxide fuel cell material BaZrO{sub 3} has been derived. Using a quantum mechanical potential energy surface, the parameters of an interatomic potential model to describe hydroxyl groups within both pure and yttrium-doped BaZrO{sub 3} have been determined. Reactivity is then incorporated through the use of the empirical valence bond model. Molecular dynamics simulations (EVB-MD) have been performed to explore the diffusion of hydrogen using a stochastic thermostat and barostat whose equations are extended to the isostress-isothermal ensemble. In the low concentration limit, the presence of yttrium is found not to significantly influence the diffusivity of hydrogen, despite the proton having a longer residence time at oxygen adjacent to the dopant. This lack of influence is due to the fact that trapping occurs infrequently, even when the proton diffuses through octahedra adjacent to the dopant. The activation energy for diffusion is found to be 0.42 eV, in good agreement with experimental values, though the prefactor is slightly underestimated.

  9. Evidence for phosphorus bonding in phosphorus trichloride-methanol adduct: a matrix isolation infrared and ab initio computational study.

    Science.gov (United States)

    Joshi, Prasad Ramesh; Ramanathan, N; Sundararajan, K; Sankaran, K

    2015-04-09

    The weak interaction between PCl3 and CH3OH was investigated using matrix isolation infrared spectroscopy and ab initio computations. In a nitrogen matrix at low temperature, the noncovalent adduct was generated and characterized using Fourier transform infrared spectroscopy. Computations were performed at B3LYP/6-311++G(d,p), B3LYP/aug-cc-pVDZ, and MP2/6-311++G(d,p) levels of theory to optimize the possible geometries of PCl3-CH3OH adducts. Computations revealed two minima on the potential energy surface, of which, the global minimum is stabilized by a noncovalent P···O interaction, known as a pnictogen bonding (phosphorus bonding or P-bonding). The local minimum corresponded to a cyclic adduct, stabilized by the conventional hydrogen bonding (Cl···H-O and Cl···H-C interactions). Experimentally, 1:1 P-bonded PCl3-CH3OH adduct in nitrogen matrix was identified, where shifts in the P-Cl modes of PCl3, O-C, and O-H modes of CH3OH submolecules were observed. The observed vibrational frequencies of the P-bonded adduct in a nitrogen matrix agreed well with the computed frequencies. Furthermore, computations also predicted that the P-bonded adduct is stronger than H-bonded adduct by ∼1.56 kcal/mol. Atoms in molecules and natural bond orbital analyses were performed to understand the nature of interactions and effect of charge transfer interaction on the stability of the adducts.

  10. Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces.

    Science.gov (United States)

    Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-10-13

    A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn-Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn-Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn-Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the S(N)2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three

  11. Direct assessment of quantum nuclear effects on hydrogen bond strength by constrained-centroid ab initio path integral molecular dynamics

    Science.gov (United States)

    Walker, Brent; Michaelides, Angelos

    2010-11-01

    The impact of quantum nuclear effects on hydrogen (H-) bond strength has been inferred in earlier work from bond lengths obtained from path integral molecular dynamics (PIMD) simulations. To obtain a direct quantitative assessment of such effects, we use constrained-centroid PIMD simulations to calculate the free energy changes upon breaking the H-bonds in dimers of HF and water. Comparing ab initio simulations performed using PIMD and classical nucleus molecular dynamics (MD), we find smaller dissociation free energies with the PIMD method. Specifically, at 50 K, the H-bond in (HF)2 is about 30% weaker when quantum nuclear effects are included, while that in (H2O)2 is about 15% weaker. In a complementary set of simulations, we compare unconstrained PIMD and classical nucleus MD simulations to assess the influence of quantum nuclei on the structures of these systems. We find increased heavy atom distances, indicating weakening of the H-bond consistent with that observed by direct calculation of the free energies of dissociation.

  12. Coordination modes and bonding of sulfur oxides on transition metal surfaces: combined ab initio and BOC-MP results

    Science.gov (United States)

    Seller, Harrell; Shustorovich, Evgeny

    1996-02-01

    Binding energies for sulfur oxides, SO x, x = 1-3, have been determined for several coordination modes on silver, gold and palladium surfaces employing ab initio quantum chemical methods and the bond order conservation Morse potential (BOC-MP) method. SO 2 coordination was studied in the most detail. In general the agreement between the BOC-MP and ab initio binding energies is good for the (111) surfaces of silver and palladium with both methods predicting that, in the zero coverage limit, di-coordination via S,O and O,O will be more favorable energetically than mono-coordination via S. In the case of chemisorption on the Pd (110) surface the two methods agree well for the cases in which there are formulas for the BOC-MP binding energies. In going from the (111) surfaces to the (110) surfaces of silver and palladium the ab initio calculations predict that the preferred chemisorption site shifts from the bridge site to the hollow site. On the silver surfaces the net charge transferred to the adsorbate as judged from the Mulliken populations correlates roughly with the binding energy. No significant charge transfer was found on the palladium surfaces. Our SO 2 chemisorption calculations indicate that the work functions of the metal surfaces examined should increase upon mono-S adsorption, increase to a lesser extent upon di S,O adsorption and may even decrease upon di O,O adsorption. Ab initio calculations provide evidence of the existence of SO 2 surface dimers. The binding energy predicted by the BOC-MP model for SO 3 in the bridging site agrees well with the ab initio result for SO 3 di-coordinated in the long bridge of the Ag(110) surface. The methods yield similar predictions for the case of SO on silver. Our modeling provides a coherent picture consistent with many aspects of the experimental literature. We present some model predictions, particularly the di O,O coordination mode for SO 2, that require verification experimentally.

  13. Hiawatha's Valence Bonding

    CERN Document Server

    Laughlin, R B

    2004-01-01

    There is increasing circumstantial evidence that the cuprate superconductors, and correlated-electron materials generally, defy simple materials categorization because of their proximity to one or more continuous zero-temperature phase transitions. This implies that the fifteen-year confusion about the cuprates is not fundamental at all but simply overinterpreted quantum criticality--an effect that seems mysterious by virtue of its hypersensitivity to perturbations, i.e. to sample imperfections in experiment and small modifications of approximation schemes in theoretical modeling, but is really just an unremarkable phase transition of some kind masquerading as something important, a sheep in wolf's clothing. This conclusion is extremely difficult for most physicists even to think about because it requires admitting that an identifiable physical phenomenon might cause the scientific method to fail in some cases. For this reason I have decided to explain the problem in a way that is nonthreatening, easy to read...

  14. Linear optical properties and their bond length dependence of yttrium bromide from ab initio and density functional theory calculations

    Energy Technology Data Exchange (ETDEWEB)

    Alipour, Mojtaba, E-mail: malipour@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Mohajeri, Afshan, E-mail: amohajeri@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

    2011-08-25

    Graphical abstract: The electronic properties such as the static dipole polarizability, anisotropy of the polarizability, and dipole moment of yttrium bromide, YBr (X{sup 1}{Sigma}) have been theoretically studied. Highlights: {yields} Conventional ab initio and density functional theory methods were employed to study linear optical properties of YBr molecule. {yields} Properties derivatives and their level of theory dependence were studied. {yields} Electron correlation effects and rovibrational corrections have also been discussed. - Abstract: We have employed conventional ab initio and density functional theory methods to study the electronic properties such as the mean static dipole polarizability, {alpha}-bar, anisotropy of the polarizability, {Delta}{alpha}, and dipole moment, {mu}, of yttrium bromide. The bond length dependence of properties is determined at different levels of theory and appropriate expansions around experimental internuclear distance have been presented. Moreover, the first and second geometrical derivatives for each property are quantified and their level of theory dependence has been analyzed. To study the effect of molecular rotation and vibration on the electronic properties, the rovibrational corrections have also been carried out. It is found that these corrections are less pronounced for considered properties of YBr. In all calculations, the electron correlation effects have been considered and discussed. The obtained results show that the electron correlation is more significant in the calculation of the mean and the anisotropy of dipole polarizability.

  15. π-Hydrogen Bonding of Aromatics on the Surface of Aerosols: Insights from Ab Initio and Molecular Dynamics Simulation.

    Science.gov (United States)

    Feng, Ya-Juan; Huang, Teng; Wang, Chao; Liu, Yi-Rong; Jiang, Shuai; Miao, Shou-Kui; Chen, Jiao; Huang, Wei

    2016-07-14

    Molecular level insight into the interaction between volatile organic compounds (VOCs) and aerosols is crucial for improvement of atmospheric chemistry models. In this paper, the interaction between adsorbed toluene, one of the most significant VOCs in the urban atmosphere, and the aqueous surface of aerosols was studied by means of combined molecular dynamics simulations and ab initio quantum chemistry calculations. It is revealed that toluene can be stably adsorbed on the surface of aqueous droplets via hydroxyl-π hydrogen bonding between the H atoms of the water molecules and the C atoms in the aromatic ring. Further, significant modifications on the electrostatic potential map and frontier molecular orbital are induced by the solvation effect of surface water molecules, which would affect the reactivity and pathway of the atmospheric photooxidation of toluene. This study demonstrates that the surface interactions should be taken into consideration in the atmospheric chemical models on oxidation of aromatics.

  16. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy, and ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Śmiałek, M. A., E-mail: smialek@pg.gda.pl [Department of Control and Energy Engineering, Faculty of Ocean Engineering and Ship Technology, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Łabuda, M.; Guthmuller, J. [Department of Theoretical Physic and Quantum Information, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Hubin-Franskin, M.-J.; Delwiche, J. [Département de Chimie, Université de Liège, Institut de Chimie-Bât. B6C, B-4000 Liège (Belgium); Duflot, D. [Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM), UMR CNRS 8523, Université Lille1 Sciences et Technologies, F-59655 Villeneuve d' Ascq Cedex (France); Mason, N. J. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Hoffmann, S. V.; Jones, N. C. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Building 1520, DK-8000 Aarhus C (Denmark); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)

    2014-09-14

    The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C{sub 2}H{sub 5}OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km)

  17. Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energy-loss spectroscopy in high-resolution transmission electron microscopy and ab initio time-dependent density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Guedj, C. [University Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Hung, L.; Sottile, F. [LSI, CNRS, CEA, École Polytechnique, F-91128 Palaiseau (France); European Theoretical Spectroscopy Facility (ETSF) (France); Zobelli, A. [LPS, CNRS and University Paris Sud, F-91405 Orsay (France); Blaise, P. [University Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); European Theoretical Spectroscopy Facility (ETSF) (France); Olevano, V. [University Grenoble Alpes, F-38000 Grenoble (France); European Theoretical Spectroscopy Facility (ETSF) (France); CNRS, Institut Néel, F-38042 Grenoble (France)

    2014-12-01

    The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.

  18. Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energy-loss spectroscopy in high-resolution transmission electron microscopy and ab initio time-dependent density-functional theory

    Science.gov (United States)

    Guedj, C.; Hung, L.; Zobelli, A.; Blaise, P.; Sottile, F.; Olevano, V.

    2014-12-01

    The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO2) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO2, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO2 may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.

  19. Ab Initio Assessment of the Bonding in Disulfonates Containing Divalent Nitrogen and Phosphorus Atoms

    DEFF Research Database (Denmark)

    Andersen, Vinca Bonde; Berg, Rolf W.; Shim, Irene

    2017-01-01

    The iminodisulfonate, [N(SO3)2]3–, and phosphinodisulfonate, [P(SO3)2]3–, ions have been investigated by performing ab initio MP2/6-311+G**calculations. The nitrogen and phosphorus atoms as part of the ions are shown to be divalent with a negative charge and two lone pairs on the nitrogen...... and phosphorus atoms. The experimentally known calcium sodium iminodisulfonate trihydrate and the analogous unknown compound calcium sodium phosphinodisulfonate trihydrate have also been investigated using the MP2/6-311+G** calculations. For the nitrogen compound, only minor changes occur in the iminodisulfonate...... phosphinodisulfonate trihydrate are quite different from those of the phosphinodisulfonate ion. For calcium sodium iminodisulfonate trihydrate, the Raman spectrum has been measured, and it compares well with the spectrum derived using HF/6-311+G** calculations....

  20. Benchmarking ab initio binding energies of hydrogen-bonded molecular clusters based on FTIR spectroscopy

    DEFF Research Database (Denmark)

    Bork, Nicolai Christian; Du, Lin; Reiman, Heidi;

    2014-01-01

    Models of formation and growth of atmospheric aerosols are highly dependent on accurate cluster binding energies. These are most often calculated by ab initio electronic structure methods but remain associated with significant uncertainties. We present a computational benchmarking study......) and compare this range to predictions from several widely used electronic structure methods, including five density functionals, Møller-Plesset perturbation theory, and five coupled cluster methods up to CCSDT quality, considering also the D3 dispersion correctional scheme. With some exceptions, we find...... that most electronic structure methods overestimate ΔG°295 K. The effects of vibrational anharmonicity is approximated using scaling factors, reducing ΔG°295 K by ca. 1.8 kJ mol(-1), whereby ΔG°295 K predictions well within the experimental range can be obtained....

  1. Is there theoretical evidence for mutual influence between halogen and pnicogen-hydride bonds? An ab initio study

    Indian Academy of Sciences (India)

    ELAHE PARVINI; MORTEZA VATANPARAST; ESMAIL VESSALLY; ALI BAHADORI

    2016-12-01

    Ab initio MP2/6-311++G(d,p) level calculations have been carried out to investigate the interplay between the halogen and pnicogen-hydride bonds in NCX...OPH₃...HMgY complexes (X = F, Cl, Br; Y = F, Cl, Br, H). The results indicated that the cooperative effects are obvious in the target complexes. These effects were considered in detail in terms of electrostatic potential, energetic, geometric, charge-transfer and electron density properties of the complexes. The values of cooperative energy (Ecoop) were ranging from −0.41 to −0.60 kJ/mol, −1.02 to −1.57 kJ/mol and −1.50 to −2.28 kJ/mol for X = F, Cl and Br, respectively. Based on many-body analysis, two and three-body terms of interaction energies have a positive contribution to the total interaction energy. It was found that the amount of charge transfer in the triads is higher than that in the corresponding dyads. AIM analyses showed that the halogen and pnicogen-hydride bonds in the triads are amplified with respect to the dyads

  2. Ab initio modeling of the bonding of benzotriazole corrosion inhibitor to reduced and oxidized copper surfaces.

    Science.gov (United States)

    Kokalj, Anton

    2015-01-01

    The bonding of benzotriazole-an outstanding corrosion inhibitor for copper-on reduced and oxidized copper surfaces is discussed on the basis of density functional theory (DFT) calculations. Calculations reveal that benzotriazole is able to bond with oxide-free and oxidized copper surfaces and on both of them it bonds significantly stronger to coordinatively unsaturated Cu sites. This suggests that benzotriazole is able to passivate the reactive under-coordinated surface sites that are plausible microscopic sites for corrosion attack. Benzotriazole can adsorb in a variety of different forms, yet it forms a strong molecule-surface bond only in deprotonated form. The bonding is even stronger when the deprotonated form is incorporated into organometallic adcomplexes. This is consistent with existing experimental evidence that benzotriazole inhibits corrosion by forming protective organometallic complexes. It is further shown that adsorption of benzotriazole considerably reduces the metal work function, which is a consequence of a large permanent molecular dipole and a properly oriented adsorption structure. It is argued that such a pronounced effect on the work function might be relevant for corrosion inhibition, because it should diminish the anodic corrosion reaction, which is consistent with existing experimental evidence that benzotriazole, although a mixed type inhibitor, predominantly affects the anodic reaction.

  3. Proton NMR Chemical Shift Behavior of Hydrogen-Bonded Amide Proton of Glycine-Containing Peptides and Polypeptides as Studied by ab initio MO Calculation

    Directory of Open Access Journals (Sweden)

    I. Ando

    2002-08-01

    Full Text Available Abstract: NMR chemical shifts of the amide proton of a supermolecule, an Nmethylacetamide hydrogen-bonded with a formamide, were calculated as functions of hydrogen-bond length RN…O and hydrogen-bond angles by FPT-GIAO method within the framework of HF/STO 6-31++G(d,p ab initio MO method. The calculations explained reasonably the experimental data reported previously that the isotropic proton chemical shifts move downfield with a decrease in RN…O. Further, the behavior of proton chemical shift tensor components depending on the hydrogen-bond length and hydrogen-bond angle was discussed.

  4. Periodic regularities in bonding, coordination modes and reactivity of sulfur oxides on transition metal surfaces: Combined BOC-MP and ab initio results

    Energy Technology Data Exchange (ETDEWEB)

    Shustorovich, E. [Blue Planet Technologies Co., New York, NY (United States); Sellers, H. [South Dakota State Univ., Brookings, SD (United States)

    1995-12-01

    A combination of theoretical methods (BOC-MP and high quality ab initio calculations) has been employed to understand the nature of bonding, coordination modes and reactivity of sulfur oxides on metal fcc (111), (100), (110) surfaces along the periodic series Cu, Pt, Pd and Ni. The emphasis was on the molecular chemisorption of SO{sub 2} and its dissociative pathways: S + 20 <--- SO + O <--- SO{sub 2} --- > SO{sub 3} --- > SO{sub 4}. M

  5. Ab Initio -Based Bond Order Potential to Investigate Low Thermal Conductivity of Stanene Nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Cherukara, Mathew J. [Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Sciences Division; Narayanan, Badri [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Kinaci, Alper [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Sasikumar, Kiran [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Gray, Stephen K. [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Univ. of Chicago, IL (United States). Computation Inst.; Chan, Maria K. Y. [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Univ. of Chicago, IL (United States). Computation Inst.; Sankaranarayanan, Subramanian K. R. S. [Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials; Univ. of Chicago, IL (United States). Computation Inst.

    2016-08-28

    We introduce a bond order potential (BOP) for stanene based on an ab initio derived training data set. The potential is optimized to accurately describe the energetics, as well as thermal and mechanical properties of a free-standing sheet, and used to study diverse nanostructures of stanene, including tubes and ribbons. As a representative case study, using the potential, we perform molecular dynamics simulations to study stanene’s structure and temperature-dependent thermal conductivity. We find that the structure of stanene is highly rippled, far in excess of other 2-D materials (e.g., graphene), owing to its low in-plane stiffness (stanene: ~ 25 N/m; graphene: ~ 480 N/ m). The extent of stanene’s rippling also shows stronger temperature dependence compared to that in graphene. Furthermore, we find that stanene based nanostructures have significantly lower thermal conductivity compared to graphene based structures owing to their softness (i.e., low phonon group velocities) and high anharmonic response. Our newly developed BOP will facilitate the exploration of stanene based low dimensional heterostructures for thermoelectric and thermal management applications.

  6. Ab Initio Treatment of Bond-Breaking Reactions: Accurate Course of HO3 Dissociation and Revisit to Isomerization.

    Science.gov (United States)

    Varandas, A J C

    2012-02-14

    An efficient scheme is devised for accurate studies of bond-breaking/forming reactions and illustrated for HO3. It is suggested and numerically demonstrated that an accurate dissociation path for the title system can be obtained by defining the central OO bond as the reaction coordinate. The approach consists of optimizing the dissociation path at the full-valence-complete-active space level of theory followed by single-point multireference configuration interaction calculations along it. Using large diffusely augmented basis sets of the correlation consistent type, accurate dissociation curves are then obtained for both the cis- and trans-HO3 isomers by extrapolating the calculated raw energies to the complete basis set limit. The profiles show a weak van der Waals type minimum and a small barrier, both lying below the dissociation asymptote. It is shown that this barrier arises at the break-off of the central OO chemical bond and onset of the OH···O2 hydrogen bond. The calculated dissociation energies (De) are 4.5 ± 0.1 and 4.7 ± 0.1 kcal mol(-1) for the cis- and trans-HO3 isomers, respectively, with a very conservative estimate of the dissociation energy (D0) for trans-HO3 being 2.7 ± 0.2 kcal mol(-1) and a more focused one being 2.8 ± 0.1 kcal mol(-1). This result improves upon our previous estimate of this quantity while overlapping in the lower range of 2.9 ± 0.1 kcal mol(-1), the commonly accepted value from the low-temperature CRESU experiments. Since the cis-HO3 isomer is predicted to be 0.15 kcal mol(-1) less stable than trans-HO3, this may partly explain the failure to obtain a clear characterization of the former. The isomerization (torsional) potential is also revisited and a comparison presented with a curve inferred from spectroscopic measurements. Good agreement is observed, with the accuracy of the new calculated data commending its use for the reanalysis of the available vibrational-rotational spectroscopic data.

  7. Valency and molecular structure

    CERN Document Server

    Cartmell, E

    1977-01-01

    Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t

  8. Valence and conduction band edges of selenide and sulfide-based kesterites—a study by x-ray based spectroscopy and ab initio theory

    Science.gov (United States)

    Olar, Tetiana; Manoharan, Archana; Draxl, Claudia; Calvet, Wolfram; Ümsur, Bünyamin; Parvan, Vladimir; Chacko, Binoy; Xie, Haibing; Saucedo, Edgardo; Valle-Rios, Laura Elisa; Neldner, Kai; Schorr, Susan; Lux-Steiner, Martha Ch; Lauermann, Iver

    2017-10-01

    Thin film solar cells based on the kesterite material with the general composition Cu2ZnSn(Se,S)4 can be a substitute for the more common chalcopyrites (Cu(In,Ga)(Se,S)2) with a similar band gap range. When replacing the anion sulfide with selenide, the optical band gap of kesterite changes from 1.5 to 1 eV. Here we report on a study of the valence band maximum and conduction band minimum energies of kesterites with either S or Se as the anion. Knowing these positions is crucial for the design of solar cells in order to match the bands of the absorber material with those of the subsequent functional layers like buffer or window layer. Their relative positions were studied using photoelectron spectroscopy of the valence band edge and x-ray absorption spectroscopy of the cations Cu, Zn, and Sn, respectively. The experimental results are interpreted and confirmed in terms of calculations based on density-functional theory and the GW approach of the many-body theory.

  9. H /D isotope effect on the dihydrogen bond of NH4+⋯BeH2 by ab initio path integral molecular dynamics simulation

    Science.gov (United States)

    Hayashi, Aiko; Shiga, Motoyuki; Tachikawa, Masanori

    2006-11-01

    In order to investigate the H /D isotope effect on a dihydrogen bonded cation system, we have studied NH4+⋯BeH2 and its isotopomers by ab initio path integral molecular dynamics. It is found that the dihydrogen bond can be exchanged by NH4+ rotation. The deuterated isotopomer (ND4+⋯BeD2; DD) can exchange the dihydrogen bond more easily than other isotopomers such as (NH4+⋯BeH2; HH). This unusual isotope effect is ascribed to the "quantum localization" which occurs when the effective energy barrier for the rotational mode becomes higher by the zero point energy of other modes. We also found that the binding energy of dihydrogen bonds for DD species is the smallest among the isotopomers.

  10. Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer.

    Science.gov (United States)

    Small, David W; Head-Gordon, Martin

    2017-07-14

    The Coupled Cluster Valence Bond (CCVB) method, previously presented for closed-shell (CS) systems, is extended to open-shell (OS) systems. The theoretical development is based on embedding the basic OS CCVB wavefunction in a fictitious singlet super-system. This approach reveals that the OS CCVB amplitude equations are quite similar to those of CS CCVB, and thus that OS CCVB requires the same level of computational effort as CS CCVB, which is an inexpensive method. We present qualitatively correct CCVB potential energy curves for all low-lying spin states of P2 and Mn2(+). CCVB is successfully applied to the low-lying spin states of some model linear polycarbenes, systems that appear to be a hindrance to standard density functionals. We examine an octa-carbene dimer in a side-by-side orientation, which, in the monomer dissociation limit, exhibits maximal strong correlation over the length of the polycarbene.

  11. Qgui: A high-throughput interface for automated setup and analysis of free energy calculations and empirical valence bond simulations in biological systems.

    Science.gov (United States)

    Isaksen, Geir Villy; Andberg, Tor Arne Heim; Åqvist, Johan; Brandsdal, Bjørn Olav

    2015-07-01

    Structural information and activity data has increased rapidly for many protein targets during the last decades. In this paper, we present a high-throughput interface (Qgui) for automated free energy and empirical valence bond (EVB) calculations that use molecular dynamics (MD) simulations for conformational sampling. Applications to ligand binding using both the linear interaction energy (LIE) method and the free energy perturbation (FEP) technique are given using the estrogen receptor (ERα) as a model system. Examples of free energy profiles obtained using the EVB method for the rate-limiting step of the enzymatic reaction catalyzed by trypsin are also shown. In addition, we present calculation of high-precision Arrhenius plots to obtain the thermodynamic activation enthalpy and entropy with Qgui from running a large number of EVB simulations.

  12. Atomic Structure and Valence: Level II, Unit 10, Lesson 1; Chemical Bonding: Lesson 2; The Table of Elements: Lesson 3; Electrolysis: Lesson 4. Advanced General Education Program. A High School Self-Study Program.

    Science.gov (United States)

    Manpower Administration (DOL), Washington, DC. Job Corps.

    This self-study program for high-school level contains lessons on: Atomic Structure and Valence, Chemical Bonding, The Table of Elements, and Electrolysis. Each of the lessons concludes with a Mastery Test to be completed by the student. (DB)

  13. Bond dissociation mechanism of ethanol during carbon nanotube synthesis via alcohol catalytic CVD technique: Ab initio molecular dynamics simulation

    Science.gov (United States)

    Oguri, Tomoya; Shimamura, Kohei; Shibuta, Yasushi; Shimojo, Fuyuki; Yamaguchi, Shu

    2014-03-01

    Dissociation of ethanol on a nickel cluster is investigated by ab initio molecular dynamics simulation to reveal the bond dissociation mechanism of carbon source molecules during carbon nanotube synthesis. C-C bonds in only CHxCO fragments are dissociated on the nickel cluster, whereas there is no preferential structure among the fragments for C-O bond dissociation. The dissociation preference is uncorrelated with the bond dissociation energy of corresponding bonds in freestanding molecules but is correlated with the energy difference between fragment molecules before and after dissociation on the nickel surface. Moreover, carbon-chain formation occurs after C-C bond dissociation in a continuous simulation. What determines the chirality of CNTs? What happens at the dissociation stage of carbon source molecules? Regarding the former question, many researchers have pointed out the good epitaxial relationship between a graphite network and a close-packed facet (i.e., fcc(1 1 1) or hcp(0 0 0 1)) of transition metals [17-19]. Therefore, the correlation between the chirality of CNTs and the angle of the step edge on metal (or metal carbide) surfaces has been closely investigated [20-22]. In association with this geometric matching, the epitaxial growth of graphene on Cu(1 1 1) and Ni(1 1 1) surfaces has recently been achieved via CCVD technique [23-25], which is a promising technique for the synthesis of large-area and monolayer graphene.Regarding the latter question, it is empirically known that the yield and quality of CNT products strongly depend on the choice of carbon source molecules and additives. For example, it is well known that the use of ethanol as carbon source molecules yields a large amount of SWNTs without amorphous carbons (called the alcohol CCVD (ACCVD) technique) compared with the CCVD process using hydrocarbons [4]. Moreover, the addition of a small amount of water dramatically enhances the activity and lifetime of the catalytic metal (called the

  14. Proton transfer through hydrogen bonds in two-dimensional water layers: A theoretical study based on ab initio and quantum-classical simulations

    Energy Technology Data Exchange (ETDEWEB)

    Bankura, Arindam; Chandra, Amalendu, E-mail: amalen@iitk.ac.in [Department of Chemistry, Indian Institute of Technology, Kanpur 208016 (India)

    2015-01-28

    The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.

  15. Proton transfer through hydrogen bonds in two-dimensional water layers: A theoretical study based on ab initio and quantum-classical simulations

    Science.gov (United States)

    Bankura, Arindam; Chandra, Amalendu

    2015-01-01

    The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.

  16. Valence state driven site preference in the quaternary compound Ca5MgAgGe5: an electron-deficient phase with optimized bonding.

    Science.gov (United States)

    Ponou, Siméon; Lidin, Sven; Zhang, Yuemei; Miller, Gordon J

    2014-05-05

    The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma-Wyckoff sequence c(12) with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å(3), Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R(2+n)T2X(2+n), previously described with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm-Wyckoff sequence f(5)c(2). The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.

  17. Valence State Driven Site Preference in the Quaternary Compound Ca5MgAgGe5: An Electron-Deficient Phase with Optimized Bonding

    Energy Technology Data Exchange (ETDEWEB)

    Ponou, Simeon [Centre for Analysis and Synthesis, Lund University; Lidin, Sven [Centre for Analysis and Synthesis, Lund University; Zhang, Yuemei [Ames Laboratory; Miller, Gordon J. [Ames Laboratory

    2014-04-18

    The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma – Wyckoff sequence c12 with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å3, Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R2+nT2X2+n, previously described with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm – Wyckoff sequence f5c2. The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.

  18. Equilibrium CO bond lengths

    Science.gov (United States)

    Demaison, Jean; Császár, Attila G.

    2012-09-01

    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 Å within the full range of 1.10-1.43 Å, corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  19. Emergence of string valence-bond-solid state in the frustrated J1-J2 transverse field Ising model on the square lattice

    Science.gov (United States)

    Sadrzadeh, M.; Haghshenas, R.; Jahromi, S. S.; Langari, A.

    2016-12-01

    We investigate the ground-state nature of the transverse field Ising model on the J1-J2 square lattice at the highly frustrated point J2/J1=0.5 . At zero field, the model has an exponentially large degenerate classical ground state, which can be affected by quantum fluctuations for nonzero field toward a unique quantum ground state. We consider two types of quantum fluctuations, harmonic ones by using linear spin-wave theory (LSWT) with single-spin-flip excitations above a long-range magnetically ordered background and anharmonic fluctuations, by employing a cluster-operator approach (COA) with multispin cluster-type fluctuations above a nonmagnetic cluster-ordered background. Our findings reveal that the harmonic fluctuations of LSWT fail to lift the extensive degeneracy as well as signaling a violation of the Hellmann-Feynman theorem. However, the string-type anharmonic fluctuations of COA are able to lift the degeneracy toward a string valence-bond-solid (VBS) state, which is obtained from an effective theory consistent with the Hellmann-Feynman theorem as well. Our results are further confirmed by implementing numerical tree tensor network simulation. The emergent nonmagnetic string VBS phase is gapped and breaks lattice rotational symmetry with only twofold degeneracy, which bears a continuous quantum phase transition at Γ /J1≅0.50 to the quantum paramagnet phase of high fields. The critical behavior is characterized by ν ≅1.0 and γ ≅0.33 exponents.

  20. First-order superfluid to valence-bond solid phase transitions in easy-plane SU (N ) magnets for small N

    Science.gov (United States)

    D'Emidio, Jonathan; Kaul, Ribhu K.

    2016-02-01

    We consider the easy-plane limit of bipartite SU (N ) Heisenberg Hamiltonians, which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For N =2 the easy plane limit of the SU(2) Heisenberg model is the well-known quantum X Y model of a lattice superfluid. We introduce a logical method to generalize the quantum X Y model to arbitrary N , which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of N colors in which neighboring loops are disallowed from having the same color. In this loop representation we design an efficient Monte Carlo cluster algorithm for our model. We present extensive numerical results for these models on the two dimensional square lattice, where we find the nearest neighbor model has superfluid order for N ≤5 and valence-bond order for N >5 . By introducing SU (N ) easy-plane symmetric four-spin couplings we are able to tune across the superfluid-VBS phase boundary for all N ≤5 . We present clear evidence that this quantum phase transition is first order for N =2 and N =5 , suggesting that easy-plane deconfined criticality runs away generically to a first-order transition for small N .

  1. Synthesis, Characterization Studies and Bond Valence Sum (BVS analysis on 2:1 Adducts involving Zinc(IIdithiocarbamates and 4,4’-Bipyridine

    Directory of Open Access Journals (Sweden)

    Arumugam Manohar

    2015-06-01

    Full Text Available 2:1 adducts involving [Zn(dtc2]2 (dtc- = pipdtc-, H10C5NCS-2; dnpdtc-, (H3CCH2CH22NCS-2; dedtc-, (H5C22NCS-2; dmdtc-, (H3C2NCS-2; nmedtc-, HOCH2CH2(CH3NCS-2; deadtc-, (HOCH2CH22NCS-2 and 4,4' – bipyridine were prepared and characterized by elemental analyses, IR, UV-Visible, Cyclic voltammetric and thermal studies. IR spectra of the complexes show the reduction in the thioureide stretching frequency due to the increase in coordination around the zinc ion and the resultant increase in electron density. The charge transfer transitions are observed in the region 260 – 320 nm by electronic spectra. Thermal studies show a single stage weight loss. The cyclic voltammetric study on the complexes show an increase of electron density on zinc in the adducts compared to [Zn(dtc2]2. The bond valence sum(BVS analysis shows the values to be close to '2', which is equivalent to the formal oxidation state of zinc in the zinc complexes.

  2. A minimalistic approach to static and dynamic electron correlations: Amending generalized valence bond method with extended random phase approximation correlation correction

    Science.gov (United States)

    Chatterjee, Koushik; Pastorczak, Ewa; Jawulski, Konrad; Pernal, Katarzyna

    2016-06-01

    A perfect-pairing generalized valence bond (GVB) approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems. In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation (ERPA). On the examples of systems of diverse electronic structures, we show that the resulting ERPA-GVB method greatly improves upon the GVB model. ERPA-GVB recovers most of the electron correlation and it yields energy barrier heights of excellent accuracy. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play.

  3. Rare beryllium icosahedra in the intermediate valence compound CeBe13.

    Science.gov (United States)

    Wilson, Zakiya S; Macaluso, Robin T; Bauer, E D; Smith, J L; Thompson, J D; Fisk, Z; Stanley, George G; Chan, Julia Y

    2004-11-01

    Single-crystal X-ray diffraction experiments show that the Be atoms in CeBe13 form a Be12 icosahedra, which is a very unusual structural feature due, in part, to the remarkably low valence electron count of Be. Magnetization studies show that CeBe13 displays intermediate valence behavior, in which valence fluctuations between the Ce 4f0 and 4f1 states give rise to enhanced electronic specific heat and magnetic susceptibility. Calculations using ab initio theory were used to determine the electronic structure and bonding and to give insight into the relationship between the crystal structure, the bonding, and the intermediate valence behavior of CeBe13. The hybridization between the localized f electrons and the conduction electrons is responsible for the large values of the electronic specific heat coefficient (gamma approximately 100 mJ/mol K2) and magnetic susceptibility (chi approximately 1 x 10-3 emu/mol), which is in marked contrast to those of ordinary metals that have gamma approximately 1 mJ/mol K2 and chi approximately 1 x 10-5 emu/mol values. The magnetic susceptibility, chi = M/H versus T, of a single crystal of CeBe13 exhibits a broad maximum at Tmax approximately 130 K and is typical of intermediate valence systems with an unusually large energy scale (Kondo), TK approximately 500 K.

  4. Hydrogen Bonding in Ion-pair Molecules in Vapors over ionic liquids, studied by Raman Spectroscopy and ab initio Calculations

    DEFF Research Database (Denmark)

    Berg, Rolf W.

    -H-Br] [ref 2] and (3) the 1-methylimidazolium ethano-ate, [mim-H-O2CCH3] found [ref 3] to have a less likely existence in the vapor of the corresponding liquid in ampouls at ~200°C (Fig. 2). Experimental Raman results will be compared to ab initio calculated spectra. Fig. 1. Likely gaseous ion pair molecule...

  5. Polysulfide anions II: structure and vibrational spectra of the S4(2-) and S5(2-) anions. Influence of the cations on bond length, valence, and torsion angle.

    Science.gov (United States)

    el Jaroudi, O; Picquenard, E; Demortier, A; Lelieur, J P; Corset, J

    2000-06-12

    The influence of the cations on bond length, valence, and torsion angle of S4(2-) and S5(2-) anions was examined in a series of solid alkali tetra- and pentasulfides by relating their Raman spectra to their known X-ray structures through a force-field analysis. The IR and Raman spectra of BaS4.H2O and the Raman spectra of (NH4)2S4.nNH3, gamma-Na2S4, and delta-Na2S5 are presented. The similarity of spectra of gamma-Na2S4 with those of BaS4.H2O suggests similar structures of the S4(2-) anions in these two compounds with a torsion angle smaller than 90 degrees. The variations of SS bond length, SSS valence angle, and dihedral angle of Sn2- anions are related to the polarization of the lone pair and electronic charge of the anion by the electric field of the cations. A correlation between the torsion angle and the SSS valence angle is shown as that previously reported between the length of the bond around which the torsion takes place and the dihedral angle value. These geometry changes are explained by the hyperconjugation concept and the electron long-pair repulsion.

  6. Vibrational progressions in the valence ionizations of transition metal hydrides: evaluation of metal-hydride bonding and vibrations in (eta(5)-C(5)R(5))Re(NO)(CO)H [R = H, CH(3)].

    Science.gov (United States)

    Lichtenberger, Dennis L; Gruhn, Nadine E; Rai-Chaudhuri, Anjana; Renshaw, Sharon K; Gladysz, John A; Jiao, Haijun; Seyler, Jeff; Igau, Alain

    2002-02-20

    The first examples of vibrational structure in metal-ligand sigma-bond ionizations are observed in the gas-phase photoelectron spectra of CpRe(NO)(CO)H and CpRe(NO)(CO)H [Cp = eta(5)-C(5)H(5), Cp = eta(5)-C(5)(CH(3))(5)]. The vibrational progressions are due to the Re-H stretch in the ion states formed by removal of an electron from the predominantly Re-H sigma-bonding orbitals. A vibrational progression is also observed in the corresponding ionization of the deuterium analogue, CpRe(NO)(CO)D, but with lower vibrational energy spacing as expected from the reduced mass effect. The vibrational progressions in these valence ionizations are directly informative about the nature of the metal-hydride bonding and electronic structure in these molecules. Franck-Condon analysis shows that for these molecules the Re-H or Re-D bond lengthens by 0.25(1) A when an electron is removed from the Re-H or Re-D sigma-bond orbital. This bond lengthening is comparable to that of H(2) upon ionization. Removal of an electron from the Re-H or Re-D bonds leads to a quantum-mechanical inner sphere reorganization energy (lambda(QM)) of 0.34(1) eV. These observations suggest that even in these low symmetry molecules the orbital corresponding to the Re-H sigma bond and the Re-H vibrational mode is very localized. Theoretical calculations of the electronic structure and normal vibrational modes of CpRe(NO)(CO)H support a localized two-electron valence bond description of the Re-H interaction.

  7. High Valence, Normal Valence and Unknown Valence

    DEFF Research Database (Denmark)

    Morsing, Thorbjørn Juul

    )3]+ with X = Cl and Br. The extreme kinetic robustness of the Ir(III) centers prevents chloride abstraction by Ag(I) and the unusual complexes are formed instead. A ligand eld and ab initio study of the ligand complexes [IrX3(NCCH3)3] is performed and compared to the silver complexes and it is found...... of for instance incorporating the carbide functionality into other systems. Several chapters and papers include X-ray spectroscopy measurements and a very brief introduction to the techniques is given in Appendix A. Throughout the thesis computational studies of various kinds have been used to help...... the elucidation of experimental observations and a brief study on the computation of ligand eld transitions in transition metal complexes is given in Appendix B....

  8. Energetics and bonding study of hexamethylenetetramine and fourteen related cage molecules: An ab initio G3(MP2 investigation

    Directory of Open Access Journals (Sweden)

    HO-ON HO

    2005-04-01

    Full Text Available The ab initio G3(MP2method has been applied to hexamethylenetetramine (HMT and fourteen related cage systems. The agreement between the calculated and experimental molecular dimensions, which are available for five of the 15 cage species, ranges from satisfactory to excellent. In addition, the G3(MP2 heat of formation at 298 K for HMT is in excellent accord with experimental results. Hence, the calculated heats of formation for the other 14 cage systems should be reliable estimates.

  9. Ab Initio Calculations of the N-N Bond Dissociation for the Gas-phase RDX and HMX

    Science.gov (United States)

    Liu, Lin-Lin; Liu, Pei-Jin; Hu, Song-Qi; He, Guo-Qiang

    2017-01-01

    NO2 fission is a vital factor for 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) decomposition. In this study, the geometry of the gas-phase RDX and HMX molecules was optimized, and the bond order and the bond dissociation energy of the N-N bonds were examined. Moreover, the rate constants of the gas-phase RDX and HMX conformers, concerning the N-N bond dissociation, were evaluated using the microcanonical variational transition state theory (μVT). The calculation results have shown that HMX is more stable than RDX in terms of the N-N bond dissociation, and the conformers stability parameters were as follows: RDXaaa HMX I HMX II. In addition, for the RDX conformers, the N-N bond of the pseudo-equatorial positioning of the nitro group was more stable than the N-N bond of the axial positioning of the nitro group, while the results were opposite in the case of the HMX conformers. Moreover, it has been shown that the dissociation rate constant of the N-N bond is influenced by the temperature significantly, thus the rate constants were much lower (<10-10 s-1) when the temperature was less than 1000 K.

  10. Perceiving molecular themes in the structures and bonding of intermetallic phases: the role of Hückel theory in an ab initio era.

    Science.gov (United States)

    Stacey, Timothy E; Fredrickson, Daniel C

    2012-07-14

    Qualitative molecular orbital theory is central to our understanding of the bonding and reactivity of molecules and materials across chemistry. Advances in computational technology and methodology, however, have made ab initio or density functional theory calculations a simpler alternative, offering reliable results on increasingly large systems in a reasonable time-scale without the need for concerns about the approximations and parameterization of semi-empirical one-electron based methods. In this perspective, we illustrate how the availability of higher-level computational results can augment, rather than supplant, the insights provided by approaches such as the simple and extended Hückel methods. We begin by describing a way to parameterize Hückel-type Hamiltonians against DFT results for intermetallic systems. The potential for chemical understanding embodied by such orbital-based models is then demonstrated with two schemes of bonding analysis that originated in them (but can be extended to DFT results): the μ(3)-acid/base model and the μ(2)-Hückel chemical pressure analysis, which translate the molecular concepts of acidity and electronic/steric competition, respectively, into the context of intermetallic chemistry.

  11. Study on the effects of fluorine and oxygen deficiency on YBa2Cu3O7 by ab initio method

    Institute of Scientific and Technical Information of China (English)

    刘洪霖; 曹晓卫; 瞿丽曼; 陈念贻

    1997-01-01

    The calculations of clusters modeling the fluorine-doping and oxygen deficiency of YBa2Cu3O2,have been performed by the method of all-electron ab initio Hartree-Fock with self-consistent crystal field Results show that in CuO planes electric charge significantly increases,the chemical valence of Cu decreases and the covalent bonding of Cu-O greatly weakens owing to oxygen deficiency,while the effect of F restores the local electronic structure of YBa2Cu3O7 The reported opinion that F occupied the oxygen vacancy in Cu-O chains seems disputable according to the calculated bonding characteristics.

  12. Water O-H bond activation by gas-phase plutonium atoms: reaction mechanisms and ab initio molecular dynamics study.

    Science.gov (United States)

    Li, Peng; Niu, Wenxia; Gao, Tao; Wang, Hongyan

    2014-10-06

    A thorough description of the reaction mechanisms, taking into account different possible spin states, offers insights into the gas-phase reaction of plutonium atoms with water. Two possible reactions (isomerization and dehydrogenation) are presented. These reactions are found to be exothermic, with the best thermochemical conditions observed for the dehydrogenation reaction at around 23.5 kcal mol(-1). The nature of the chemical-bonding evolution along the reaction pathways are investigated by employing various methods including electron localization function, atoms in molecules, and Mayer bond order. Total, partial, and overlap population density of state diagrams and analyses are also presented. Reaction rates at elevated temperatures (T=298-2 000 K) are calculated by using variational transition-state theory with one-dimensional tunneling effects. In dynamics simulations, only the dehydrogenation reaction is observed, and found to be in good agreement with experimental values.

  13. Ab initio study of the solvent H-bonding effect on ESIPT reaction and electronic transitions of 3-hydroxychromone derivatives.

    Science.gov (United States)

    Kenfack, Cyril A; Klymchenko, Andrey S; Duportail, Guy; Burger, Alain; Mély, Yves

    2012-07-07

    The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules. To examine the effect of the H-bond on the ESIPT reaction, the absorption and emission wavelengths as well as the energies of the different states that intervene during these electronic transitions were calculated in acetonitrile, ethanol and methanol. The calculated positions of the absorption and emission wavelengths in various solvents were in excellent agreement with the experimental spectra, validating our approach. We found that in DMAF, the hydrogen bonding with protic solvents makes the ESIPT reaction energetically unfavourable, which explains the absence of the ESIPT tautomer emission in protic solvents. In contrast, the excited tautomer state of FHC remains energetically favourable in both aprotic and protic solvents. Comparing our calculations with the previously reported time-resolved fluorescence data, the ESIPT reaction of DMAF in aprotic solvents is reversible because the emitting states are energetically close, whereas in FHC, ESIPT is irreversible because the tautomer state is below the corresponding normal state. Therefore, the ESIPT reaction in DMAF is controlled by the relative energies of the excited states (thermodynamic control), while in FHC the ESIPT is controlled probably by the energetic barrier (kinetic control).

  14. Dissociation constants of weak acids from ab initio molecular dynamics using metadynamics: influence of the inductive effect and hydrogen bonding on pKa values.

    Science.gov (United States)

    Tummanapelli, Anil Kumar; Vasudevan, Sukumaran

    2014-11-26

    The theoretical estimation of the dissociation constant, or pKa, of weak acids continues to be a challenging field. Here, we show that ab initio Car-Parrinello molecular dynamics simulations in conjunction with metadynamics calculations of the free-energy profile of the dissociation reaction provide reasonable estimates of the pKa value. Water molecules, sufficient to complete the three hydration shells surrounding the acid molecule, were included explicitly in the computation procedure. The free-energy profiles exhibit two distinct minima corresponding to the dissociated and neutral states of the acid, and the difference in their values provides the estimate for pKa. We show for a series of organic acids that CPMD simulations in conjunction with metadynamics can provide reasonable estimates of pKa values. The acids investigated were aliphatic carboxylic acids, chlorine-substituted carboxylic acids, cis- and trans-butenedioic acid, and the isomers of hydroxybenzoic acid. These systems were chosen to highlight that the procedure could correctly account for the influence of the inductive effect as well as hydrogen bonding on pKa values of weak organic acids. In both situations, the CPMD metadynamics procedure faithfully reproduces the experimentally observed trend and the magnitudes of the pKa values.

  15. VB studies on bonding features of HNC(←→)HCN

    Institute of Scientific and Technical Information of China (English)

    廖新丽; 吴玮; 莫亦荣; 张乾二

    2003-01-01

    Within the bonded tableau unitary group approach (BTUGA), a scheme, combined with Pauling's resonance theory to select the predominant valence bond structures for VB calculations, is proposed. This scheme ensures a reliable and illustrative bonding picture in the description of chemical reactions, as exemplified by the isomerization reaction HNCHCN. The computation results account for important bonding features about this isomerization at the ab initio level and explore the mechanism of phenomena such as (i) HCN is more stable than HNC; (ii) the C-N bond first lengthens and then shortens in the vicinity of the transition state; (iii) only H-atom migration is observed in the isomerization process, without the breaking of the CN bond. Our results demonstrate that only a few bonded tableau functions are sufficient enough to provide a visual and reliable bonding picture.

  16. Structure, stability and bonding of (BC 2N) n, n=2,3: an ab initio study

    Science.gov (United States)

    Kar, T.; Cuma, M.; Scheiner, S.

    2000-12-01

    The dimer and trimer of BC 2N are studied at the HF and MPn levels using 3-21G, 6-31G ∗ and 6-31+G ∗ basis sets. It is found that stability is enhanced by maintaining -BN- units together in the cyclic form. Both molecules have cyclic ground state structures with cumulenic-type equal bond lengths in the -BNBN- and polyacetylenic -CCCC- fragments. The linear-cyclic energy difference increases with the size of the cluster. Electron correlation substantially favors the cyclic structures over the linear forms. No general trend of atomic combination has been found in the linear isomers. Diffuse functions have negligible effects on the relative energies and geometries of the dimers.

  17. Paired-permanent approach for VB theory (II) -An ab initio spin-free VB program

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Paired-permanent approach for VB theory is extensively developed. Canonical expan sion of a paired-permanent is deduced. Furthermore, it is shown that a paired-permanent may be expressed in terms of the products of sub-paired-permanents of any given order and their corre sponding minors. An ab initio spin-free valence bond program, called Xiamen, is implemented by using paired-permanent approach. Test calculation shows that Xiamen package is more efficient than some other programs based on the traditional VB algorithm, and it provides a new practical tool for quantum chemistry.

  18. Structural, vibrational and bonding properties of hydro-nitrogen solids under high pressure: An ab-initio study

    Indian Academy of Sciences (India)

    G VAITHEESWARAN; N YEDUKONDALU; B MOSES ABRAHAM

    2016-10-01

    Hydro-nitrogen solids are potential high energy density materials (HEDMs) due to high mass ratio of nitrogen which find wide range of applications as propellants and explosives. In the present work, we report the structural and vibrational properties of Tetramethyl Ammonium Azide (TMAA) and HydroZonium Azide(HZA) using density functional theory calculations by treating weak intermolecular interactions. The obtained ground state parameters using vdW-TS method are in good agreement with the experimental data. The pressure dependent lattice constants, compressibility and equation of state are discussed. The obtained equilibrium bulk moduli show the soft nature of these materials. The compressibility curves reveal that these compounds are highly compressible along crystallographic a-axis.We have also calculated the zone-center phonon frequencies and made a complete analysis of vibrational spectra at ambient as well as at high pressure. Contraction and elongation of C-H and N-H (NH₃ stretching) bonds under pressure lead to blue- and red-shift of the frequencies in the mid-IR region for TMAA and HZA compounds, respectively

  19. Ab initio investigation of structure, stability, thermal behavior, bonding, and infrared spectra of ionized water cluster (H2O)6+

    Science.gov (United States)

    Liu, Lei; Hu, Cui-E.; Tang, Mei; Chen, Xiang-Rong; Cai, Ling-Cang

    2016-10-01

    The low-lying isomers of cationic water cluster (H2O)6+ have been globally explored by using particle swarm optimization algorithm in conjunction with quantum chemical calculations. Compared with previous results, our searching method covers a wide range of structural isomers of (H2O)6+ and therefore turns out to be more effective. With these local minima, geometry optimization and vibrational analysis are performed for the most interesting clusters at second-order Møller-Plesset (MP2)/aug-cc-pVDZ level, and their energies are further refined at MP2/aug-cc-pVTZ and coupled-cluster theory with single, double, and perturbative triple excitations/aug-cc-pVDZ level. The interaction energies using the complete basis set limits at MP2 level are also reported. The relationships between their structure arrangement and their energies are discussed. Based on the results of thermal simulation, structural change from a four-numbered ring to a tree-like structure occurs at T ≈ 45 K, and the relative population of six lowest-free-energy isomers is found to exceed 4% at some point within the studied temperature range. Studies reveal that, among these six isomers, two new-found isomers constitute 10% of isomer population at 180 K, and the experimental spectra can be better explained with inclusions of the two isomers. The molecular orbitals for six representative cationic water clusters are also studied. Through topological and reduced density gradient analysis, we investigated the structural characteristics and the bonding strengths of these water cluster radical cations.

  20. Valence space electron momentum spectroscopy of diborane

    Energy Technology Data Exchange (ETDEWEB)

    Wang Feng [Centre for Molecular Simulation, Swinburne University of Technology, P.O. Box 218, Hawthorn, Melbourne, Vic. 3122 (Australia)]. E-mail: fwang@swin.edu.au; Pang Wenning [Department of Physics, Polarization Physics Laboratory, Tsinghua University, Beijing 100084 (China); Huang Ming [Department of Physics, Polarization Physics Laboratory, Tsinghua University, Beijing 100084 (China)

    2006-05-15

    A non-classical mechanism of binding in diborane (B{sub 2} H{sub 6}) is derived quantum-mechanically (B3LYP/6-311++G**) using a dual-space analysis. High-resolution binding-energy spectra of diborane, generated using an outer-valence Green's-function and density-functional theory with a statistical average of model orbital potentials (SAOP), agree satisfactorily with experiment. Electron-correlation energies of diborane produce orbital-based variations in ionization energy in the valence space, but with negligible impact on the shape of only a{sub g} symmetry orbitals as indicated in momentum space. The present work indicates quantitatively that (a) the pair of three-centre banana-shaped B-H{sub b}-B bonds are more accurately described as one diamond-shaped bond with B-H{sub b}-B-H{sub b}, (b) all bonds in diborane are electron-deficient including the four equivalent B-H{sub t} bonds, (c) there is no pure B?B bond but contributions from all valence orbitals form an unconventional electron-deficient B-B bond, and (d) only two innermost valence orbitals - 2a{sub g} and 2b{sub 1u} - are sp{sup 2}-hybridized and no evidence indicates other valence orbitals of diborane to be hybridized.

  1. Vibrational Properties of Hydrogen-Bonded Systems Using the Multireference Generalization to the "On-the-Fly" Electronic Structure within Quantum Wavepacket ab Initio Molecular Dynamics (QWAIMD).

    Science.gov (United States)

    Li, Junjie; Li, Xiaohu; Iyengar, Srinivasan S

    2014-06-10

    We discuss a multiconfigurational treatment of the "on-the-fly" electronic structure within the quantum wavepacket ab initio molecular dynamics (QWAIMD) method for coupled treatment of quantum nuclear effects with electronic structural effects. Here, multiple single-particle electronic density matrices are simultaneously propagated with a quantum nuclear wavepacket and other classical nuclear degrees of freedom. The multiple density matrices are coupled through a nonorthogonal configuration interaction (NOCI) procedure to construct the instantaneous potential surface. An adaptive-mesh-guided set of basis functions composed of Gaussian primitives are used to simplify the electronic structure calculations. Specifically, with the replacement of the atom-centered basis functions positioned on the centers of the quantum-mechanically treated nuclei by a mesh-guided band of basis functions, the two-electron integrals used to compute the electronic structure potential surface become independent of the quantum nuclear variable and hence reusable along the entire Cartesian grid representing the quantum nuclear coordinates. This reduces the computational complexity involved in obtaining a potential surface and facilitates the interpretation of the individual density matrices as representative diabatic states. The parametric nuclear position dependence of the diabatic states is evaluated at the initial time-step using a Shannon-entropy-based sampling function that depends on an approximation to the quantum nuclear wavepacket and the potential surface. This development is meant as a precursor to an on-the-fly fully multireference electronic structure procedure embedded, on-the-fly, within a quantum nuclear dynamics formalism. We benchmark the current development by computing structural, dynamic, and spectroscopic features for a series of bihalide hydrogen-bonded systems: FHF(-), ClHCl(-), BrHBr(-), and BrHCl(-). We find that the donor-acceptor structural features are in good

  2. A highly accurate {\\it ab initio} potential energy surface for methane

    CERN Document Server

    Owens, Alec; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter

    2016-01-01

    A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art \\textit{ab initio} theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include: core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of $^{12}$CH$_4$ reproduced with a root-mean-square error of $0.70{\\,}$cm$^{-1}$. The computed \\textit{ab initio} equilibrium C{--}H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as $J$ (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the e...

  3. Levels of Valence

    Science.gov (United States)

    Shuman, Vera; Sander, David; Scherer, Klaus R.

    2013-01-01

    The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

  4. VB studies on bonding features of HNCHCN

    Institute of Scientific and Technical Information of China (English)

    LIAO; Xinli(

    2003-01-01

    [1]Skurski, P., Gutowski, M., Simons, J., Ab initio electronic structure of HCN- and HNC-dipole-bound anions and a description of electron loss upon tautomerization, J. Chem. Phys., 2001, 114(17): 7443-7449.[2]Jursic, B. S., Complete basis set ab initio study of potential energy surfaces of the dissociation recombination reaction HCNH++e(-), J. Mol. Struct., 1999, 487(3): 211-220.[3]Abashkin, Y., Russo, N., Toscano, M., Transition states and energy barriers from density functional studies: representative isomerization reactions, Int. J. Quantum Chem., 1994, 52: 695-704.[4]Bentley, J. A., Bowman, J. M., Gazdy, B. et al., A global ab initio potential for HCN/HNC exact vibrational energies and comparision to experiment, Chem. Phys. Lett., 1992, 198(6): 563-569.[5]Bentley, J. A., Huang, C. M., Wyatt, R. E., Highly vibrationally excited HCN/HNC: eigenvalues, wave functions, and stimulated emission pumping spectra, J. Chem. Phys., 1992, 98(7): 5207-5221.[6]Peric, M., Mladrenovic, M., Peyerimhoff, S. D. et al., Ab initio study of the isomerization HNC-HCN, 1. Ab initio calculation of the HNV reversible HCN potential surface and the corresponding energy-levels, Chem. Phys., 1983, 82: 317-336.[7]Zhang, Q. E., Li, X. Z., Bonded tableau method for many-electron systems, J. Mol. Struct. (Theochem.), 1989, 198: 413-425.[8]Li, X. Z., Zhang, Q. E., Bonded tableau unitary group approach to the many-electron correlation problem, Int. J. Quantum Chem., 1989, 36: 599-632.[9]Li, J. B., Wu, W., New algorithm for nonorthogonal ab initio valence-bond calculations, Theor. Chim. Acta, 1994, 89: 105-121.[10]Wu, W., Mo, Y. R., Zhang, Q. E., On the resonance theory, J. Mol. Struct., 1993, 283: 227-236.[11]Mo, Y. R., Wu, W., Zhang, Q. E., Valence bond description for the ground state and several low-lying excited states of LiH, J. Mol. Struct., 1993, 283: 237-249.[12]Pauling, L., The Nature of Chemical Bond, 3rd ed., Ithaca, New York: Cornell

  5. An ab initio study of the C2H2-HF, C2H(CH3)-HF and C2(CH3)2-HF hydrogen-bonded complexes.

    Science.gov (United States)

    Ramos, Mozart N; Lopes, Kelson C; Silva, Washington L V; Tavares, Alessandra M; Castriani, Fátima A; do Monte, Silmar A; Ventura, Elizete; Araújo, Regiane C M U

    2006-02-01

    MP2/6-31++G** and B3LYP/6-31++G** ab initio molecular orbital calculations have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the C2H2-HF, C2H(CH3)-HF and C2(CH3)2-HF H-bonded complexes. As expected, the more pronounced effects on the structural properties of the isolated molecules due to complexation was verified for the C[triple bond]C and H-F bond lengths, which are directly involved in the H-bond formation. These bond distances increased after complexation. BSSE uncorrected B3LYP binding energies are always lower than the corresponding MP2 values. However, the opposite trend has been verified after BSSE correction by the counterpoise method since it is much lower at B3LYP than at MP2 level. The binding energies for these complexes as well as for the HF acid submolecule modes (the HF stretching and vibrational frequency modes) showed an increasing hydrogen-bonding strength with increasing methyl substitution. The splitting in the HF in-plane and out-of-plane bending modes reflects the anisotropy in the hydrogen-bonding interaction with the pi system of the C[triple bond]C bond. The H-F stretching frequency is shifted downward after complexation and it increases with the methyl substitution. The IR intensities of the HF acid submolecule fundamentals are adequately interpreted through the atomic polar tensor of the hydrogen atom using the charge-charge flux-overlap model. The skeletal stretching modes of the Alkyne submolecule are decreased in the complex. The new vibrational modes arising from complexation show several interesting features.

  6. Electronic states and nature of bonding of the molecule PdGe by all electron ab initio HF–CI calculations and mass spectrometric equilibrium experiments

    DEFF Research Database (Denmark)

    Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.

    1986-01-01

    In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...

  7. Nature of the valence excited states of bromine in the T and P clathrate cages

    Science.gov (United States)

    Batista-Romero, Fidel A.; Gamboa-Suárez, Antonio; Hernández-Lamoneda, Ramón; Janda, Kenneth C.

    2017-04-01

    The guest-host intermolecular potentials for the valence excited states of Br2 in the tetrakaidecahedral(T) and pentakaidecahedral(P) clathrate cages have been calculated using ab initio local correlation methods. We find that the excited states are more strongly bound than the corresponding ground states even in the small T cage where bromine has a tight fit. The angular dependence of the interaction energies is quite anisotropic; this reflects in the corresponding electronic shifts where regions of maxima for blue-shifts in the T cage indicate the presence of halogen bonding. We predict a large temperature dependence of the electronic shifts and compare absolute values with recent experimental studies. This stringent test indicates the reliability of local correlation treatments to describe weak intermolecular forces in ground and excited states.

  8. Coulombic Models in Chemical Bonding.

    Science.gov (United States)

    Sacks, Lawrence J.

    1986-01-01

    Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

  9. Highly efficient perturbative + variational strategy based on orthogonal valence bond theory for the evaluation of magnetic coupling constants. Application to the trinuclear Cu(ii) site of multicopper oxidases.

    Science.gov (United States)

    Tenti, Lorenzo; Maynau, Daniel; Angeli, Celestino; Calzado, Carmen J

    2016-07-21

    A new strategy based on orthogonal valence-bond analysis of the wave function combined with intermediate Hamiltonian theory has been applied to the evaluation of the magnetic coupling constants in two AF systems. This approach provides both a quantitative estimate of the J value and a detailed analysis of the main physical mechanisms controlling the coupling, using a combined perturbative + variational scheme. The procedure requires a selection of the dominant excitations to be treated variationally. Two methods have been employed: a brute-force selection, using a logic similar to that of the CIPSI approach, or entanglement measures, which identify the most interacting orbitals in the system. Once a reduced set of excitations (about 300 determinants) is established, the interaction matrix is dressed at the second-order of perturbation by the remaining excitations of the CI space. The diagonalization of the dressed matrix provides J values in good agreement with experimental ones, at a very low-cost. This approach demonstrates the key role of d → d* excitations in the quantitative description of the magnetic coupling, as well as the importance of using an extended active space, including the bridging ligand orbitals, for the binuclear model of the intermediates of multicopper oxidases. The method is a promising tool for dealing with complex systems containing several active centers, as an alternative to both pure variational and DFT approaches.

  10. Molecular Orbital, Generalized Valence Bond, and Complete Active Space Calculations on Transition Metal Compounds with Agostic Hydrogen and Bridging Carbonyls: New Basis Sets, Geometry of Trichloromethyltitanium, and Bonding of bis

    Science.gov (United States)

    Williamson, Rodney Lowell

    Total geometry optimizations are reported for Cr(CO)_6, HMn(CO)_5 , Fe(CO)_5, Ni(CO) _4, Cr(C_6H _6)_2, Fe(C_5H _5)_2, Ni(C_4 H_4)_2, Cr(NO) _4, (C_5H _5)Mn(CO)_3, and (C _6H_6)Cr(CO) _3. A variety of basis sets were examined, and, based on the results, a relatively compact and accurate basis set is proposed. Addition of electron correlation at the perfect pairing GVB level reduced the average difference in the metal-cyclopentadienyl bond length of 0.08 A. Optimization of the geometry of TiCl_4 and TiCl_3CH_3 at the self-consistent-field (SCF) level results in Ti-Cl bond lengths longer than the experimental values, even when d- and f-type polarization functions are added to the basis set. The bond lengths remain too long even as the Hartree-Fock limit is approached because the SCF level of theory over-estimates the noble-gas-like Cl cdotsCl repulsions, which hinder close Ti -Cl approach. The Ti-C-H angle of TiCl_3 CH_3 is calculated to be close to tetrahedral geometry with little flattening of the hydrogen atoms, which apparently was observed in the electron diffraction. These same calculations do predict the anomalously low methyl-rocking frequency for the titanium complex in agreement with the experimental IR. The large positive geminal hydrogen coupling constant observed in the NMR experiment is due primarily to the sigma -donor and pi-acceptor character of the TiCl_3 moiety and not to any flattening of the methyl group. The structure and bonding of (Cr(Cp)(CO) _2) _2 was examined by optimizing the geometry of the dimer, fragment moiety, and analogous stable monomers. The optimized structure of Cr(Cp)(CO)_2N has a "piano stool" geometry with a fragment moiety geometry nearly identical to the geometry of the fragment moiety in the dimer. Examination of x-ray and theoretical geometries of monomers with the fragment moiety bonded to single ligand show that the geometry of the fragment moiety is insensitive to the ligands bonded to it. Van der Waals calculations

  11. Ab initio structures for 90 degrees -twisted s-trans-1,3-butadiene and cyclooctatetraene: the naked sp2-sp2 bond.

    Science.gov (United States)

    Feller, David; Craig, Norman C; Matlin, Albert R

    2008-03-20

    The bond length of a carbon-carbon sp2-sp2 sigma-bond without the perturbing effects of pi-interactions has been estimated by high level calculations on two prototypical systems: a 90 degrees -twisted form of butadiene and the tub conformer of cyclooctatetraene. The former system yields a value of 1.4818 A, considerably longer than previous estimates. The corresponding bond length in the latter is slightly shorter due to some pi-electron delocalization.

  12. Electronic states and nature of bonding in the molecule YC by all electron ab initio multiconfiguration self-consistent-field calculations and mass spectrometric equilibrium experiments

    DEFF Research Database (Denmark)

    Shim, Irene; Pelino, Mario; Gingerich, Karl A.

    1992-01-01

    , and they hardly contribute to the bonding. The chemical bond in the YC molecule is polar with charge transfer from Y to C giving rise to a dipole moment of 3.90 D at 3.9 a.u. in the 4PI ground state. Mass spectrometric equilibrium investigations in the temperature range 2365-2792 K have resulted...

  13. Valence state parameters of all transition metal atoms in metalloproteins--development of ABEEMσπ fluctuating charge force field.

    Science.gov (United States)

    Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia

    2014-09-05

    To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy.

  14. Beryllium dimer: a bond based on non-dynamical correlation.

    Science.gov (United States)

    El Khatib, Muammar; Bendazzoli, Gian Luigi; Evangelisti, Stefano; Helal, Wissam; Leininger, Thierry; Tenti, Lorenzo; Angeli, Celestino

    2014-08-21

    The bond nature in beryllium dimer has been theoretically investigated using high-level ab initio methods. A series of ANO basis sets of increasing quality, going from sp to spdf ghi contractions, has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculations with several different active spaces. The quality of these calculations has been checked by comparing the results with valence Full-CI calculations, performed with the same basis sets. It is shown that two quasi-degenerated partly occupied orbitals play a crucial role to give a qualitatively correct description of the bond. Their nature is similar to that of the edge orbitals that give rise to the quasi-degenerated singlet-triplet states in longer beryllium chains.

  15. Ab initio study of the electronic structure andelastic properties of Al5C3N

    Institute of Scientific and Technical Information of China (English)

    Xu Xue-Wen; Hu Long; Yu Xiao; Lu Zun-Ming; Fan Ying; Li Yang-xian; Tang Cheng-Chun

    2011-01-01

    We investigate the electronic structure,chemical bonding and elastic properties of the hexagonal aluminum carbonitride,Al5C3N,by ab initio calculations.Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV.The valence bands below the Fermi level (EF) originate from the hybridized Al p-C p and Al p-N p states.The calculated bulk and Young's moduli are 201 GPa and 292 GPa,which are slightly lower than those of Ti3SiC2.The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97,respectively,which axe higher than those of Ti2AlCand Ti2AlN,indicating that Al5C3N is a ductile ceramic.

  16. AB-INITIO SIMULATION OF ELECTRONIC FEATURES OF HYPERFINE RARE EARTH OXIDE FILMS FOR SENSORY NANOSYSTEMS

    Directory of Open Access Journals (Sweden)

    A. V. Gulay

    2014-01-01

    Full Text Available Ab-Initio simulation of electronic features of sensoring nanomaterials based on rare earth oxides has been made by the example of yttrium oxide. The simulation method for thin films of nanometer scale consisted in the simulation of the material layer of the thickness equal to unit crystal cell size has been proposed within the VASP simulation package. The atomic bond breakdown in the crystal along one of the coordinate axes is simulated by the increase of a distance between the atomic layers along this axis up to values at which the value of free energy is stabilized. It has been found that the valence and conductivity bands are not revealed explicitly and the band gap is not formed in the hyperfine rare earth oxide film (at the film thickness close to 1 nm. In fact the hyperfine rare earth oxide film loses dielectric properties which were exhibited clear enough in continuum.

  17. Electronic structure and bonding in the RhC molecule by all-electron ab initio HF–Cl calculations and mass spectrometric measurements

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, K. A.

    1984-01-01

    in a singly occupied, nonbonding orbital. The chemical bond in RhC is polar with a charge transfer from Rh to C giving rise to a dipole moment of 2.82 D at the experimental equilibrium distance. Mass spectrometric equilibrium measurements over the temperature range 1970–2806 K have resulted in the selected...

  18. Bond—Valence Sum and Distortion of Coordination Polyhedra

    Institute of Scientific and Technical Information of China (English)

    章礼明

    1993-01-01

    By using the Lagrange's intermediate value theorem,it is derived mathematically that the structur-al distortion of a coordination polyhedron may lead to an increase in bond-valence sum of the cen-tral atom of ion .The applicabilities of the bond-valence model are discussed in the following two cases:the modeling of crystal structure ,and the indication of distortion degree of a coordination polyhedron.Also it is shown that a distorted polyhedron should be in favor of a longer average bond length or a smaller coordination number.

  19. Ab initio MO study on equilibrium bond distance between Fe and pyridine in bis(pyridine)(porphinato) iron for various electronic states

    Science.gov (United States)

    Saito, Minoru; Kashiwagi, Hiroshi

    1985-04-01

    For bis(pyridine)(porphinato) iron [FeP(py)2], a correlation between the iron electronic state and the equilibrium Fe-Npy distance was investigated. Potential energy curves as a function of the Fe-Npy distance were calculated for low-spin, intermediate-spin, and high-spin states of the ferric and ferrous ions by the ab initio SCF MO method. The equilibrium Fe-Npy distances were obtained from the potential curves. The values obtained for the ferric low-spin and high-spin states were in good agreement with the experimental values for Fe(III)(OEP)(3-Clpy)2 within the differences, ±0.05 Å. The following significant features were found. The equilibrium distance is elongated by the occupation of the 3dz2 orbital and is shortened by the oxidation of the iron atom. The distance and the force constant for the symmetrical py-Fe-py stretching are strongly correlated with the overlap population between the 3dz2 orbital and pyridine-nitrogen orbitals.

  20. Interaction of a pseudo-π C—C bond with cuprous and argentous chlorides: Cyclopropane⋯CuCl and cyclopropane⋯AgCl investigated by rotational spectroscopy and ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Zaleski, Daniel P.; Mullaney, John C.; Bittner, Dror M.; Walker, Nicholas R., E-mail: a.c.legon@bristol.ac.uk, E-mail: nick.walker@newcastle.ac.uk [School of Chemistry, Newcastle University, Bedson Building, Newcastle-Upon-Tyne NE1 7RU (United Kingdom); Tew, David P.; Legon, Anthony C., E-mail: a.c.legon@bristol.ac.uk, E-mail: nick.walker@newcastle.ac.uk [School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom)

    2015-10-28

    Strongly bound complexes (CH{sub 2}){sub 3}⋯MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH{sub 2}){sub 3}⋯CuCl and (CH{sub 2}){sub 3}⋯AgCl. The geometry of each of these complexes was established unambiguously to have C{sub 2v} symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C{sub 3} triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH{sub 2}){sub 3}⋯MCl. The M atom interacts with the pseudo-π bond linking the pair of equivalent carbon atoms {sup F}C (F = front) nearest to it, so that M forms a non-covalent bond to one C—C edge of the cyclopropane molecule. The (CH{sub 2}){sub 3}⋯MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH{sub 2}){sub 3}⋯HCl and (CH{sub 2}){sub 3}⋯ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12*)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the {sup F}C—{sup F}C bond and the shrinkage of the two equivalent {sup B}C—{sup F}C (B = back) bonds relative to the C—C bond in cyclopropane itself. The expansions of the {sup F}C—{sup F}C bond are 0

  1. Valence electron theory of graphite spheroidizing in primary crystallization

    Institute of Scientific and Technical Information of China (English)

    刘志林; 孙振国; 李志林

    1995-01-01

    Bond-length-difference (BLD) analysis results show that austenrte and cementite containing Mg, Zr. S have very different valence electron structures from Fe -C austenite and cementite. We find that this difference is the tie of absorption hypothesis, surface tension hypothesis, undercooling hypothesis in graphite spheroidizing theory. By using "the model of valence electron theory of drag-like effect" in our previous paper in crystallization theory, the spheroidizing effect of Mg and Zr and the anti-spheroidizing effect of S can be explained with the valence electron structure data of phases. Therefore, electron theory of graphite spheroidizing can be advanced.

  2. NMR J-Coupling Constants of Tl-Pt Bonded Metal Complexes in Aqueous Solution: Ab Initio Molecular Dynamics and Localized Orbital Analysis.

    Science.gov (United States)

    Ducati, Lucas C; Marchenko, Alex; Autschbach, Jochen

    2016-11-21

    The influence of solvent (water) coordination and dynamics on the electronic structure and nuclear magnetic resonance (NMR) indirect spin-spin coupling (J-coupling) constants in a series of Tl-Pt bonded complexes is investigated using Kohn-Sham (KS) Car-Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations with and without coordination to water. Coordination of the Tl center by water molecules has a dramatic impact on (1)J(Tl-Pt) and other J-coupling constants. It is shown that a previous computational study of the same complexes using static optimized structures and nonhybrid functionals was correct about the important role of the solvent but obtained reasonable agreement with experimental NMR data because of a cancellation of substantial errors. For example, the CPMD trajectories show that on average the inner coordination shell of Tl is not saturated, as previously assumed, which leads to poor agreement with experiment when the J-coupling constants are averaged over the CPMD trajectories using NMR calculations with nonhybrid functionals. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of (1)J(Tl-Pt) and the correct trends for other coupling constants. An analysis of (1)J(Tl-Pt) in terms of localized orbitals shows that the presence of coordinating water molecules increases the capacity for covalent interactions between Tl and Pt. There is pronounced multicenter bonding along the metal-metal axis of the complexes.

  3. Ab initio molecular dynamics study of H-bonding and proton transfer in the phosphoric acid-N,N-Dimethylformamide system

    Science.gov (United States)

    Fedorova, Irina V.; Krestyaninov, Michael A.; Safonova, Lyubov P.

    2016-09-01

    Car-Parrinello molecular dynamics simulations of phosphoric acid (H3PO4)-N,N-dimethylformamide (DMF) mixtures over the whole composition range have been carried out. It has been found that the neutral molecules are the dominant species in this system. The concentration dependences of the average number of H-bonds per proton acceptor atom in P=O and C=O groups as well as per proton donor atom in DMFH+ ions towards phosphate species have been discussed. The H-bonding between components in all investigated mixtures of H3PO4 and DMF is possible. A significant fraction of the protonated DMF forms appears at phosphoric acid mole fraction higher than 0.37, indicating a high probability of proton transfer from phosphate species to oxygen atoms in C=O groups. The intermolecular proton transfer between phosphate species themselves is mainly observed when xH3PO4 > 0.19. Satisfactory agreement with available experimental data for structural characteristics of the investigated system was obtained.

  4. An effective scheme for selecting basis sets for ab initio calculations

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    An effective scheme for selecting economical basis sets for ab initio calculations has been proposed for wide-range systems based on the analysis of different functions in the currently used basis sets. Accordingly, the selection of the basis sets should be made according to the different properties and real chemical surrounding of the atoms in the systems. For normal systems, the size and level of the basis sets used for the descriptions of the constituent atoms should be increased from left to right according to the position of the atom in the periodic table. Moreover, the more the atom is negatively charged, the more the basis functions and suitable polarization functions and diffuse functions should be utilized. Whereas, for the positively charged atoms, the size of basis set may be reduced. It is not necessary to use the polarization and diffuse functions for the covalently saturated atoms with normal valence states. However, for the system involving hydrogen-bonding, weak interactions, functional groups, metallic bonding with zero valence or low positive valence, and other sensitive interactions, the polarization and diffuse functions must be used. With this scheme, reliable calculation results may be obtained with suitable basis sets and smaller computational capability. By detailed analysis of a series of systems, it has been demonstrated that this scheme is very practical and effective. This scheme may be used in Hartree-Fock, M?ller-Plesset and density functional theoretical calculations. It is expected that the scheme would find important applications in the extensive calculations of large systems in chemistry, materials science, and life and biological sciences.

  5. Ab Initio Investigations of the Excited Electronic States of CaOCa

    Science.gov (United States)

    Fawzy, Wafaa M.; Heaven, Michael

    2016-06-01

    Chemical bonding in alkaline earth hypermetalic oxides is of fundamental interest. Previous Ab initio studies of CaOCa predicted a centrosymmetric linear geometry for both the 1Σg^+ ground state and the low lying triplet 3Σu^+ state. However, there have been no reports concerning the higher energy singlet and triplet states. The present work is focused on characterization of the potential energy surface (PES) of the excited 1Σu^+ state (assuming a centrosymmetric linear geometry) and obtaining predictions for the 1Σu^+←1Σg^+ vibronic transitions. We employed the multireference configuration interaction (MRCISD) method with state-averaged, full-valence complete active space self-consistent field (SA-FV-CASSCF) wavefunctions. In these calculations, the active space consisted of ten valence electrons in twelve orbitals, where all the valence electrons were correlated. Contributions of higher excitation and relativistic effects were taken into account using the Davidson correction and the Douglas-Kroll (DK) Hamiltonian, respectively. The correlation-consistent polarized weighed core-valence quadruple zeta basis set (cc-pwCVQZ-DK) was used for all three atoms. The full level of theory is abbreviated as SA-FV-CASSCF (10,12)-MRCISD-Q/cc-pwCVQZ-DK. The calculations were carried out using the MOLPRO2012 suite of programs. For the centrosymmetric linear geometry in all states, initial investigations of one-dimensional radial cuts provided equilibrium bond distances of 2.034 {Å}, 2.034 {Å}, and 1.999 {Å} for the 1Σg^+ , 3Σu^+ , and 1Σu^+ states, respectively. The vertical excitation frequency of the 1Σu^+←1Σg^+ optical transition was calculated to occur at 14801 wn. These predictions were followed by spectroscopic searches by Heaven et al. Indeed, rotationally resolved vibronic progressions were recorded in the vicinity of the predicted electronic band origin. Calculation of the three-dimensional PES showed that the potential minimum in the 1Σu^+ corresponds

  6. The essential role of charge-shift bonding in hypervalent prototype XeF2

    Science.gov (United States)

    Braïda, Benoît; Hiberty, Philippe C.

    2013-05-01

    Hypervalency in XeF2 and isoelectronic complexes is generally understood in terms of the Rundle-Pimentel model (which invokes a three-centre/four-electron molecular system) or its valence bond version as proposed by Coulson, which replaced the old expanded octet model of Pauling. However, the Rundle-Pimentel model is not always successful in describing such complexes and has been shown to be oversimplified. Here using ab initio valence bond theory coupled to quantum Monte Carlo methods, we show that the Rundle-Pimentel model is insufficient by itself in accounting for the great stability of XeF2, and that charge-shift bonding, wherein the large covalent-ionic interaction energy has the dominant role, is a major stabilizing factor. The energetic contribution of the old expanded octet model is also quantified and shown to be marginal. Generalizing to isoelectronic systems such as ClF3, SF4, PCl5 and others, it is suggested that charge-shift bonding is necessary, in association with the Rundle-Pimentel model, for hypervalent analogues of XeF2 to be strongly bonded.

  7. The elusive ≡C-H· · ·O complex in the hydrogen bonded systems of Phenylacetylene: A Matrix Isolation Infrared and Ab Initio Study

    Indian Academy of Sciences (India)

    GINNY KARIR; MARIYAM FATIMA; K S VISWANATHAN

    2016-10-01

    Hydrogen-bonded complexes of phenylacetylene (PhAc) with methanol (MeOH) and diethylether (DEE) were studied using matrix isolation infrared spectroscopy. This study specifically searched for the ≡CH · · ·O hydrogen bonded complex in these systems, which manifest a n-σ* interaction and which is a local minimum on the PhAc-MeOH potential surface, as in the case of PhAc-H2O heterodimer. This n-σ* local minimum eluded observation in gas phase studies and it was therefore thought interesting to look for this isomer in cryogenic matrices.While MeOH can interact with PhAc as both a proton donor (O-H· · ·π complex) or a proton acceptor (n-σ* complex), DEE can only manifest the n-σ* isomer. A comparison of the spectral shifts observed in the features of PhAc-MeOH and PhAc-DEE would therefore independently confirm the existence or not of n-σ* complex in both these systems. In addition to the n-σ* complex observed in both the above systems, the O-H· · · π complex was also discerned in the PhAc-MeOH system. These complexes have stabilization energy in the range of 8-25 kJ/mol. The experimental results were corroborated by computations performed at MP2 and M06-2X, levels of theory, using 6-311++G(d,p) and aug-cc-pVDZ basis sets. Single point calculations at the CCSD level of theory were also performed. Atoms-in-molecules (AIM), NBO and LMOEDA analysis were also performed to understand the nature of the intermolecular interactions in these complexes.

  8. Getting down to the Fundamentals of Hydrogen Bonding: Anharmonic Vibrational Frequencies of (HF)2 and (H2O)2 from Ab Initio Electronic Structure Computations.

    Science.gov (United States)

    Howard, J Coleman; Gray, Jessica L; Hardwick, Amanda J; Nguyen, Linh T; Tschumper, Gregory S

    2014-12-09

    This work presents a systematic investigation into the basis set convergence of harmonic vibrational frequencies of (H2O)2 and (HF)2 computed with second-order Møller-Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles method with perturbative connected triples, CCSD(T), while employing correlation-consistent basis sets as large as aug-cc-pV6Z. The harmonic vibrational frequencies presented here are expected to lie within a few cm(-1) of the complete basis set (CBS) limit. For these important hydrogen-bonding prototype systems, a basis set of at least quadruple-ζ quality augmented with diffuse functions is required to obtain harmonic vibrational frequencies within 10 cm(-1) of the CBS limit. In addition, second-order vibrational perturbation theory (VPT2) anharmonic corrections yield CCSD(T) vibrational frequencies in excellent agreement with experimental spectra, differing by no more than a few cm(-1) for the intramonomer fundamental vibrations. D0 values predicted by CCSD(T) VPT2 computations with a quadruple-ζ basis set reproduce the experimental values of (HF)2 and (H2O)2 to within 2 and 21 cm(-1), respectively.

  9. Modelling the local atomic structure of molybdenum in nuclear waste glasses with ab initio molecular dynamics simulations.

    Science.gov (United States)

    Konstantinou, Konstantinos; Sushko, Peter V; Duffy, Dorothy M

    2016-09-21

    The nature of chemical bonding of molybdenum in high level nuclear waste glasses has been elucidated by ab initio molecular dynamics simulations. Two compositions, (SiO2)57.5-(B2O3)10-(Na2O)15-(CaO)15-(MoO3)2.5 and (SiO2)57.3-(B2O3)20-(Na2O)6.8-(Li2O)13.4-(MoO3)2.5, were considered in order to investigate the effect of ionic and covalent components on the glass structure and the formation of the crystallisation precursors (Na2MoO4 and CaMoO4). The coordination environments of Mo cations and the corresponding bond lengths calculated from our model are in excellent agreement with experimental observations. The analysis of the first coordination shell reveals two different types of molybdenum host matrix bonds in the lithium sodium borosilicate glass. Based on the structural data and the bond valence model, we demonstrate that the Mo cation can be found in a redox state and the molybdate tetrahedron can be connected with the borosilicate network in a way that inhibits the formation of crystalline molybdates. These results significantly extend our understanding of bonding in Mo-containing nuclear waste glasses and demonstrate that tailoring the glass composition to specific heavy metal constituents can facilitate incorporation of heavy metals at high concentrations.

  10. Does a hydrogen bonded complex with dual contacts show synergism? A matrix isolation infrared and ab-initio study of propargyl alcohol-water complex

    Science.gov (United States)

    Saini, Jyoti; Viswanathan, K. S.

    2016-08-01

    When hydrogen bonded complexes are formed with more than one contact, the question arises if these multiple contacts operate synergistically. Propargyl alcohol-H2O complex presents a good case study to address this question, which is discussed in this work. Complexes of propargyl alcohol (PA) and H2O were studied experimentally using matrix isolation infrared spectroscopy, which was supported by quantum chemical computations performed at the M06-2X and MP2 level of theories, using 6-311++G (d,p) and aug-cc-pVDZ basis sets. A 1:1 PA-H2O complex was identified in the experiments and corroborated by our computations, where the PA was in the gauche conformation. This complex, which was a global minimum, showed dual interactions, one of which was an n-σ interaction between the O-H group of PA and the O of H2O, while the second was a H···​π contact between the O-H group of H2O and the π system of PA. We explored if the two interactions in the 1:1 complex exhibited synergism. We finally argue that the two interactions showed antagonism rather than synergism. Our computations indicated three other local minima for the 1:1 complexes; though these local minima were not identified in our experiments. Atoms-in-molecules and energy decomposition analysis executed through LMO-EDA were also performed to understand the nature of intermolecular interactions in the PA-H2O complexes. We have also revisited the problem of conformations of PA, with a view to understanding the reasons for gauche conformational preferences in PA.

  11. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of nickel carbide (NiC) and its cation (NiC+).

    Science.gov (United States)

    Lau, Kai-Chung; Chang, Yih Chung; Shi, Xiaoyu; Ng, C Y

    2010-09-21

    The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D(0)) and heats of formation at 0 K (ΔH(o)(f0)) and 298 K (ΔH(o)(f298)) for NiC and NiC(+) are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC(+) to be (1)∑(+) and (2)∑(+), respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D(0)(Ni-C)-D(0)(Ni(+)-C). The analysis of the correction terms shows that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of NiC/NiC(+). For the experimental D(0) and ΔH(o)(f0) values of

  12. Micro-Valences: Affective valence in neutral everyday objects

    Directory of Open Access Journals (Sweden)

    Sophie eLebrecht

    2012-04-01

    Full Text Available Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses. Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the majority of objects carry some affective valence (micro-valences and, thus, nominally neutral objects are not really neutral. Functionally, the perception of valence in everyday objects facilitates perceptually-driven choice behavior, decision-making, and affective responses.

  13. Phonon spectra of elpasolites Cs2NaRF6 (R=Y,Yb): Ab initio calculations

    Science.gov (United States)

    Chernyshev, Vladimir; Petrov, Vladislav; Nikiforov, Anatoliy; Zakiryanov, Dmitriy

    2015-12-01

    The influence of hydrostatic pressure on structure and dynamics of a crystal lattice of elpasolites Cs2NaYbF6 and Cs2NaYF6 (S.G. 225) within ab initio approach is investigated. Frequencies and irreducible representations (irreps) of phonon modes are determined. Elastic constants are calculated. The calculations are carried out within MO LCAO approach using DFT method with hybrid functionalities of B3LYP and PBE0 in CRYSTAL09 periodic code. For the description of rare earth ion the pseudopotential replacing internal orbitals including 4f orbitals was used. External 5s and 5p orbitals defining chemical bond were described by valence basis sets.

  14. Phonon spectra of elpasolites Cs{sub 2}NaRF{sub 6} (R=Y,Yb): Ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Chernyshev, Vladimir, E-mail: Vladimir.Chernyshev@urfu.ru; Petrov, Vladislav; Nikiforov, Anatoliy; Zakiryanov, Dmitriy [Ural Federal University, Ekaterinburg (Russian Federation)

    2015-12-07

    The influence of hydrostatic pressure on structure and dynamics of a crystal lattice of elpasolites Cs{sub 2}NaYbF{sub 6} and Cs{sub 2}NaYF{sub 6} (S.G. 225) within ab initio approach is investigated. Frequencies and irreducible representations (irreps) of phonon modes are determined. Elastic constants are calculated. The calculations are carried out within MO LCAO approach using DFT method with hybrid functionalities of B3LYP and PBE0 in CRYSTAL09 periodic code. For the description of rare earth ion the pseudopotential replacing internal orbitals including 4f orbitals was used. External 5s and 5p orbitals defining chemical bond were described by valence basis sets.

  15. Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations

    Directory of Open Access Journals (Sweden)

    Hamsa Naji Nasir

    2012-01-01

    Full Text Available Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.

  16. Nucleus-Dependent Valence-Space Approach to Nuclear Structure

    Science.gov (United States)

    Stroberg, S. R.; Calci, A.; Hergert, H.; Holt, J. D.; Bogner, S. K.; Roth, R.; Schwenk, A.

    2017-01-01

    We present a nucleus-dependent valence-space approach for calculating ground and excited states of nuclei, which generalizes the shell-model in-medium similarity renormalization group to an ensemble reference with fractionally filled orbitals. Because the ensemble is used only as a reference, and not to represent physical states, no symmetry restoration is required. This allows us to capture three-nucleon (3 N ) forces among valence nucleons with a valence-space Hamiltonian specifically targeted to each nucleus of interest. Predicted ground-state energies from carbon through nickel agree with results of other large-space ab initio methods, generally to the 1% level. In addition, we show that this new approach is required in order to obtain convergence for nuclei in the upper p and s d shells. Finally, we address the 1+/3+ inversion problem in 22Na and 46V. This approach extends the reach of ab initio nuclear structure calculations to essentially all light- and medium-mass nuclei.

  17. YNi and its hydrides: Phase stabilities, electronic structures and chemical bonding properties from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Matar, S.F., E-mail: matar@icmcb-bordeaux.cnrs.fr [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France); Nakhl, M. [Universite Libanaise, Laboratoire de Chimie-Physique des Materiaux LCPM, Fanar (Lebanon); Al Alam, A.F.; Ouaini, N. [Universite Saint-Esprit de Kaslik, Faculte des Sciences et de Genie Informatique, Jounieh (Lebanon); Chevalier, B. [CNRS, Universite de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, F-33608 Pessac (France)

    2010-11-25

    Graphical abstract: Base centered orthorhombic YNiH{sub X} structure. For x = 3, only H1 and H2 are present. Highest hydrogen content YNiH{sub 4} is obtained when H3 are added. - Abstract: Within density functional theory, establishing the equations of states of YNi in two different controversial structures in the literature, leads to determine the orthorhombic FeB-type as the ground state one with small energy difference. For YNiH{sub 3} and YNiH{sub 4} hydrides crystallizing in the orthorhombic CrB-type structure the geometry optimization and the ab initio determination of the H atomic positions show that the stability of hydrogen decreases from the tri- to the tetra- hydride. New states brought by hydrogen within the valence band lead to its broadening and to enhanced localization of metal density of states. The chemical bonding analysis shows a preferential Ni-H bonding versus Y-H.

  18. Exocyclic push-pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2- exo-methylene- and 2-cyanoimino-quinazolines and -benzodiazepines

    Science.gov (United States)

    Benassi, R.; Bertarini, C.; Hilfert, L.; Kempter, G.; Kleinpeter, E.; Spindler, J.; Taddei, F.; Thomas, S.

    2000-03-01

    The structure of a number of 2- exo-methylene substituted quinazolines and benzodiazepines, respectively, 1, 3a, b, 4( X=-CN, -COOEt ) and their 2-cyanoimino substituted analogues 2, 3c, d( X=-CN, -SO 2C 6H 4-Me (p) was completely assigned by the whole arsenal of 1D and 2D NMR spectroscopic methods. The E/ Z isomerism at the exo-cyclic double bond was determined by both NMR spectroscopy and confirmed by ab initio quantum chemical calculations; the Z isomer is the preferred one, its amount proved dependent on steric hindrance. Due to the push-pull effect in this part of the molecules the restricted rotation about the partial C 2,C 11 and C 2,N 11 double bonds, could also be studied and the barrier to rotation measured by dynamic NMR spectroscopy. The free energies of activation of this dynamic process proved very similar along the compounds studied but being dependent on the polarity of the solvent. Quantum chemical calculations at the ab initio level were employed to prove the stereochemistry at the exo-cyclic partial double bonds of 1- 4, to calculate the barriers to rotation but also to discuss in detail both the ground and the transition state of the latter dynamic process in order to better understand electronic, inter- and intramolecular effects on the barrier to rotation which could be determined experimentally. In the cyanoimino substituted compounds 2, 3c, d, the MO ab initio calculations evidence the isomer interconversion to be better described by the internal rotation process than by the lateral shift mechanism.

  19. A diabatic representation including both valence nonadiabatic interactions and spin-orbit effects for reaction dynamics.

    Science.gov (United States)

    Valero, Rosendo; Truhlar, Donald G

    2007-09-06

    provides a multibond generalization of the switch between Hund's cases in diatomic spectroscopy. The spin-orbit matrix elements in this representation are taken equal to their atomic values times a scaling function that depends on the internuclear distances. The spin-valence diabatic potential energy matrix is suitable for semiclassical dynamics simulations. Diagonalization of this matrix produces the spin-coupled adiabatic energies. For the sake of illustration, diabatic potential energy matrices are constructed along bond-fission coordinates for the HBr and the BrCH(2)Cl molecules. Comparison of the spin-coupled adiabatic energies obtained from the spin-valence diabatics with those obtained by ab initio calculations with geometry-dependent spin-orbit matrix elements shows that the new method is sufficiently accurate for practical purposes. The method formulated here should be most useful for systems with a large number of atoms, especially heavy atoms, and/or a large number of spin-coupled electronic states.

  20. Structure, magnetism, and theoretical study of a mixed-valence Co(II)3Co(III)4 heptanuclear wheel: lack of SMM behavior despite negative magnetic anisotropy.

    Science.gov (United States)

    Chibotaru, Liviu F; Ungur, Liviu; Aronica, Christophe; Elmoll, Hani; Pilet, Guillaume; Luneau, Dominique

    2008-09-17

    A mixed-valence Co(II)/Co(III) heptanuclear wheel [Co(II)3Co(III)4(L)6(MeO)6] (LH2 = 1,1,1-trifluoro-7-hydroxy-4-methyl-5-aza-hept-3-en-2-one) has been synthesized and its crystal structure determined using single-crystal X-ray diffraction. The valence state of each cobalt ion was established by bond valence sum calculations. Studies of the temperature dependence of the magnetic susceptibility and the field dependence of the magnetization evidence ferromagnetic interactions within the compound. In order to understand the magnetic properties of this Co7 wheel, we performed ab initio calculations for each cobalt fragment at the CASSCF/CASPT2 level, including spin-orbit coupling effects within the SO-RASSI approach. The four Co(III) ions were found to be diamagnetic and to give a significant temperature-independent paramagnetic contribution to the susceptibility. The spin-orbit coupling on the three Co(II) sites leads to separations of approximately 200 cm(-1) between the ground and excited Kramers doublets, placing the Co7 wheel into a weak-exchange limit in which the lowest electronic states are adequately described by the anisotropic exchange interaction between the lowest Kramers doublets on Co(II) sites. Simulation of the exchange interaction was done within the Lines model, keeping the fully ab initio treatment of magnetic anisotropy effects on individual cobalt fragments using a recently developed methodology. A good description of the susceptibility and magnetization was obtained for nearest-neighbor (J1) and next-nearest-neighbor (J2) exchange parameters (1.5 and 5.5 cm(-1), respectively). The strong ferromagnetic interaction between distant cobalt ions arises as a result of low electron-promotion energies in the exchange bridges containing Co(III) ions. The calculations showed a large value of the magnetization along the main magnetic axis (10.1 mu(B)), which is a combined effect of the ferromagnetic exchange interaction and negative magnetic anisotropy on

  1. On the hierarchical parallelization of ab initio simulations

    CERN Document Server

    Ruiz-Barragan, Sergi; Shiga, Motoyuki

    2016-01-01

    A hierarchical parallelization has been implemented in a new unified code PIMD-SMASH for ab initio simulation where the replicas and the Born-Oppenheimer forces are parallelized. It is demonstrated that ab initio path integral molecular dynamics simulations can be carried out very efficiently for systems up to a few tens of water molecules. The code was then used to study a Diels-Alder reaction of cyclopentadiene and butenone by ab initio string method. A reduction in the reaction energy barrier is found in the presence of hydrogen-bonded water, in accordance with experiment.

  2. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

    This is the perfect complement to ""Chemical Bonding - Across the Periodic Table"" by the same editors, who are two of the top scientists working on this topic, each with extensive experience and important connections within the community. The resulting book is a unique overview of the different approaches used for describing a chemical bond, including molecular-orbital based, valence-bond based, ELF, AIM and density-functional based methods. It takes into account the many developments that have taken place in the field over the past few decades due to the rapid advances in quantum chemica

  3. Reactive Force Fields via Explicit Valency

    Science.gov (United States)

    Kale, Seyit

    Computational simulations are invaluable in elucidating the dynamics of biological macromolecules. Unfortunately, reactions present a fundamental challenge. Calculations based on quantum mechanics can predict bond formation and rupture; however they suffer from severe length- and time-limitations. At the other extreme, classical approaches provide orders of magnitude faster simulations; however they regard chemical bonds as immutable entities. A few exceptions exist, but these are not always trivial to adopt for routine use. We bridge this gap by providing a novel, pseudo-classical approach, based on explicit valency. We unpack molecules into valence electron pairs and atomic cores. Particles bear ionic charges and interact via pairwise-only potentials. The potentials are informed of quantum effects in the short-range and obey dissociation limits in the long-range. They are trained against a small set of isolated species, including geometries and thermodynamics of small hydrides and of dimers formed by them. The resulting force field captures the essentials of reactivity, polarizability and flexibility in a simple, seamless setting. We call this model LEWIS, after the chemical theory that inspired the use of valence pairs. Following the introduction in Chapter 1, we initially focus on the properties of water. Chapter 2 considers gas phase clusters. To transition to the liquid phase, Chapter 3 describes a novel pairwise long-range compensation that performs comparably to infinite lattice summations. The approach is suited to ionic solutions in general. In Chapters 4 and 5, LEWIS is shown to correctly predict the dipolar and quadrupolar response in bulk liquid, and can accommodate proton transfers in both acid and base. Efficiency permits the study of proton defects at dilutions not accessible to experiment or quantum mechanics. Chapter 6 discusses explicit valency approaches in other hydrides, forming the basis of a reactive organic force field. Examples of simple

  4. The effective valence shell Hamiltonian calculations of spin-orbit splittings in small diatomic hydrides.

    Science.gov (United States)

    Chang, Ye Won; Sun, Hosung

    2008-12-18

    Recently, the size extensive, ab initio effective valence shell Hamiltonian method for spin-orbit coupling has been suggested. In essence, this effective Hamiltonian method is equivalent to the quasidegenerate perturbation theory. But the difference lies in transforming the original Hamiltonian into an effective Hamiltonian acting within a relatively small valence in the effective valence shell Hamiltonian method. One advantage of the method is that the spin-orbit coupling energies of all valence states for both the neutral species and its ions are simultaneously determined with a similar accuracy from a single computation of the effective spin-orbit coupling operator. Thus, fine structure splittings are predicted for a number of states of each system for which neither experiment nor theory is available. To assess the accuracy of the effective Hamiltonian method more extensively, test calculations are performed for the spin-orbit splittings in the valence states of small diatomic hydrides and their ions. The calculated spin-orbit splittings are generally in good agreement with experiments and with other ab initio computations.

  5. Effect of pressure on the lattice structure and dynamics of elpasolites Cs2Na RF6 ( R = Y, Yb): ab initio calculation

    Science.gov (United States)

    Chernyshev, V. A.; Petrov, V. P.; Nikiforov, A. E.; Zakir'yanov, D. O.

    2015-06-01

    The effect of hydrostatic compression on the lattice structure and dynamics of elpasolites Cs2NaYbF6 and Cs2NaYF6 (sp. gr. 225) has been investigated ab initio. The frequencies and types of fundamental oscillations are determined, and elastic constants are calculated. The computation is performed within the molecular orbitals-linear combinations of atomic orbitals (MO LCAO) approach using the density functional theory (DFT) method with hybrid functionals B3LYP and PBE0 in the CRYSTAL09 program. The rare-earth ion was described by representing the inner (in particular, 4 f) orbitals in the form of a pseudopotential. The outer 5 s and 5 p orbitals, which determine chemical bonding, were described using valence basis sets.

  6. 若干氢键团簇的纳秒和飞秒激光光电离及从头计算研究%Nanosecond and Femtosecond Laser Photoionization and Ab Initio Calculation Studies of Some Hydrogen Bonded Clusters

    Institute of Scientific and Technical Information of China (English)

    张柏林; 楼南泉; 王秀岩

    2003-01-01

    The multiphoton ionization and dissociation of azabenzenes-solvent clusters were studied using a time-of-flight mass spectrometer, nano- and femtosecond lasers. Due to the fact that the problem was resolved technically, the experiments about multiphoton ionization of pyrimidine-water in gas phase were performed successfully. The multiphoton ionization mass spectroscopy of the clusters was observed for the first time. The experimental results indicate sequences of protonated cluster ions are formed. Based on both ab initio calculations results and dependence of cluster ion intensity on the laser power, the processes of proton transfer and charge transfer within the clusters were presented. During the femtosecond laser photonionization of pyridine clusters, the coexistencephenomena of protonated and unprotonated cluster ions was observed first. The existence of pyridine dimmer ions and relevant calculation results indicate that the C-H…Nbonds can be formed between pyridine molecules, which corrected some reported results and also provided with a good example for the study of weak bond clusters. The multiphoton ionization results of pyrimidine-methanol and pyridazine-methanol clusters are presented for the first time. It is also found that only the protonated cluster ions are produced after clusters' ionization. The stable structures of all clusters were obtained theoretically, and the mechanisms and processes of proton transfer after ionization were elucidated.%利用纳秒和飞秒激光及飞行时间质谱仪对氮化苯-溶剂分子团簇的多光子电离和离解进行了研究.通过解决实验中的技术难题,实现了在气相条件下实验研究嘧啶与水团簇的多光子电离.首次观测到该团簇的多光子电离质谱,发现电离后形成了质子化团簇系列,通过团簇浓度随激光强度的变化以及理论计算,阐明了团簇内质子转移过程,以及电荷分布和质子转移过程随着团簇尺寸的变化;首次观测

  7. Valence Fluctuations in La2-xSrxCuO4

    NARCIS (Netherlands)

    Groot, R.A. de; Gutfreund, H.; Weger, M.

    1987-01-01

    Ab-initio electronic band structure calculations are presented for the perovskite La2CuO4 and for this material doped with Sr for a supercell of composition La3SrCu2O8. This material is close to the high Tc superconductor La2-xSrxCuO4 discovered recently. The Sr doping gives rise to strong valence f

  8. Ab initio molecular dynamics simulation of laser melting of silicon

    NARCIS (Netherlands)

    Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.

    1996-01-01

    The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting tr

  9. An effective scheme for selecting basis sets for ab initio calculations

    Institute of Scientific and Technical Information of China (English)

    张瑞勤; 黄建华; 步宇翔; 韩克利; 李述汤; 何国钟

    2000-01-01

    An effective scheme for selecting economical basis sets for ab initio calculations has been proposed for wide-range systems based on the analysis of different functions in the currently used basis sets. Accordingly, the selection of the basis sets should be made according to the different properties and real chemical surrounding of the atoms in the systems. For normal systems, the size and level of the basis sets used for the descriptions of the constituent atoms should be increased from left to right according to the position of the atom in the periodic table. Moreover, the more the atom is negatively charged, the more the basis functions and suitable polarization functions and diffuse functions should be utilized. whereas, for the positively charged atoms, the size of basis set may be reduced. it is not necessary to use the polarization and diffuse functions for the covalently saturated atoms with normal valence states. However, for the system involving hy-drogen-bonding, weak interactions, functional

  10. The evolution of the structural, vibrational and electronic properties of the cyclic ethers - on ring size. An ab initio study

    Science.gov (United States)

    Ford, Thomas A.

    2014-09-01

    The molecular structures, vibrational spectra and atomic charges of the alicyclic ethers containing from two to five carbon atoms have been determined by means of ab initio calculations, at the level of second order Møller-Plesset perturbation theory and using Dunning's augmented correlation-consistent polarized valence triple-zeta basis set. Two isomers of the oxetane, tetrahydrofuran and tetrahydropyran molecules have been identified and their relative energies determined. Structural properties, such as the COC bond angles and the CH bond lengths, are found to increase steadily with increasing ring size and with decreasing ionization energy. The mean CH2 stretching and bending wavenumbers exhibit the reverse behaviour, while the mean wavenumbers of the CH2 wagging and twisting modes follow the same trend as the structural features. The ring mode wavenumbers vary in a less regular way. The charges of the oxygen, α-carbon and axial and equatorial α- and β-hydrogen atoms also do not show systematic dependences on ring size or ionization energy. The trends in the values of these properties have been rationalized.

  11. The use of symmetrized valence and relative motion coordinates for crystal potentials

    DEFF Research Database (Denmark)

    McMurry, H. L.; Hansen, Flemming Yssing

    1980-01-01

    Symmetrized valence coordinates are linear combinations of conventional valence coordinates which display the symmetry of a set of atoms bound by the valence bonds. Relative motion coordinates are relative translations, or relative rotations, of two or more strongly bonded groups of atoms among...... which relatively weak forces act. They are useful for expressing interactions between molecules in molecular crystals and should be chosen, also, to reflect the symmetry of the interacting groups. Since coordinates defined by these procedures possess elements of symmetry in common with the bonding...... interaction constants coupling coordinates of unlike symmetry with regard to the crystal point group are necessarily zero. They may be small, also, for coordinates which belong to different representations of the local symmetry when this is not the same as for the crystal. Procedures are given for defining...

  12. Recent achievements in ab initio modelling of liquid water

    CERN Document Server

    Khaliullin, Rustam Z

    2013-01-01

    The application of newly developed first-principle modeling techniques to liquid water deepens our understanding of the microscopic origins of its unusual macroscopic properties and behaviour. Here, we review two novel ab initio computational methods: second-generation Car-Parrinello molecular dynamics and decomposition analysis based on absolutely localized molecular orbitals. We show that these two methods in combination not only enable ab initio molecular dynamics simulations on previously inaccessible time and length scales, but also provide unprecedented insights into the nature of hydrogen bonding between water molecules. We discuss recent applications of these methods to water clusters and bulk water.

  13. Valence electronic structure of tantalum carbide and nitride

    Institute of Scientific and Technical Information of China (English)

    FAN; ChangZeng

    2007-01-01

    The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.……

  14. Valence electronic structure of tantalum carbide and nitride

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.

  15. Serine Proteases an Ab Initio Molecular Dynamics Study

    CERN Document Server

    De Santis, L

    1999-01-01

    In serine proteases (SP's), the H-bond between His-57 and Asp-102, and that between Gly-193 and the transition state intermediate play a crucial role for enzymatic function. To shed light on the nature of these interactions, we have carried out ab initio molecular dynamics simulations on complexes representing adducts between the reaction intermediate and elastase (one protein belonging to the SP family). Our calculations indicate the presence of a low--barrier H-bond between His-57 and Asp-102, in complete agreement with NMR experiments on enzyme--transition state analog complexes. Comparison with an ab initio molecular dynamics simulation on a model of the substrate--enzyme adduct indicates that the Gly-193--induced strong stabilization of the intermediate is accomplished by charge/dipole interactions and not by H-bonding as previously suggested. Inclusion of the protein electric field in the calculations does not affect significantly the charge distribution.

  16. Optimized resonating valence bond state in square lattice: correlations & excitations

    Directory of Open Access Journals (Sweden)

    Z Nourbakhsh

    2009-09-01

    Full Text Available We consider RVB state as a variational estimate for the ground state of Heisenberg antiferromagnet in square lattice. We present numerical calculation of energy, spin-spin correlation function and spin excitation spectrum. We show, that the quantum flactuations reduce of magnetization respect to Neel order. Our results are in good agreement with other methods such as spin-wave calculation and series expansions.

  17. Ab initio study of the transition-metal carbene cations

    Institute of Scientific and Technical Information of China (English)

    李吉海; 冯大诚; 冯圣玉

    1999-01-01

    The geometries and bonding characteristics of the first-row transition-metal carbene cations MCH2+ were investigated by ab initio molecular orbital theory (HF/LANL2DZ). All of MCH2+ are coplanar. In the closed shell structures the C bonds to M with double bonds; while in the open shell structures the partial double bonds are formed, because one of the σ and π orbitals is singly occupied. It is mainly the π-type overlap between the 2px orbital of C and 4px, 3dxz, orbitals of M+ that forms the π orbitals. The dissociation energies of C—M bond appear in periodic trend from Sc to Cu. Most of the calculated bond dissociation energies are close to the experimental ones.

  18. A nucleus-dependent valence-space approach to nuclear structure

    CERN Document Server

    Stroberg, S R; Hergert, H; Holt, J D; Bogner, S K; Roth, R; Schwenk, A

    2016-01-01

    We present a nucleus-dependent valence-space approach for calculating ground and excited states of nuclei, which generalizes the shell-model in-medium similarity renormalization group to an ensemble reference with fractionally filled orbitals. Because the ensemble is used only as a reference, and not to represent physical states, no symmetry restoration is required. This allows us to capture 3N forces among valence nucleons with a valence-space Hamiltonian specifically targeted to each nucleus of interest. Predicted ground-state energies from carbon through nickel agree with results of other large-space ab initio methods, generally to the 1\\% level. In addition, we show that this new approach is required in order to obtain convergence for nuclei in the upper $p$ and $sd$ shells. Finally, we address the $1^+$/$3^+$ ground-state inversion problem in $^{22}\\text{Na}$ and $^{46}\\text{V}$. This approach extends the reach of ab initio nuclear structure calculations to essentially all light- and medium-mass nuclei.

  19. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    Energy Technology Data Exchange (ETDEWEB)

    Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  20. Periodic Trends in Lanthanide Compounds through the Eyes of Multireference ab Initio Theory.

    Science.gov (United States)

    Aravena, Daniel; Atanasov, Mihail; Neese, Frank

    2016-05-01

    Regularities among electronic configurations for common oxidation states in lanthanide complexes and the low involvement of f orbitals in bonding result in the appearance of several periodic trends along the lanthanide series. These trends can be observed on relatively different properties, such as bonding distances or ionization potentials. Well-known concepts like the lanthanide contraction, the double-double (tetrad) effect, and the similar chemistry along the lanthanide series stem from these regularities. Periodic trends on structural and spectroscopic properties are examined through complete active space self-consistent field (CASSCF) followed by second-order N-electron valence perturbation theory (NEVPT2) including both scalar relativistic and spin-orbit coupling effects. Energies and wave functions from electronic structure calculations are further analyzed in terms of ab initio ligand field theory (AILFT), which allows one to rigorously extract angular overlap model ligand field, Racah, and spin-orbit coupling parameters directly from high-level ab initio calculations. We investigated the elpasolite Cs2NaLn(III)Cl6 (Ln(III) = Ce-Nd, Sm-Eu, Tb-Yb) crystals because these compounds have been synthesized for most Ln(III) ions. Cs2NaLn(III)Cl6 elpasolites have been also thoroughly characterized with respect to their spectroscopic properties, providing an exceptionally vast and systematic experimental database allowing one to analyze the periodic trends across the lanthanide series. Particular attention was devoted to the apparent discrepancy in metal-ligand covalency trends between theory and spectroscopy described in the literature. Consistent with earlier studies, natural population analysis indicates an increase in covalency along the series, while a decrease in both the nephelauxetic (Racah) and relativistic nephelauxetic (spin-orbit coupling) reduction with increasing atomic number is calculated. These apparently conflicting results are discussed on the

  1. Influence of water on anharmonicity, stability, and vibrational energy distribution of hydrogen-bonded adducts in atmospheric reactions: case study of the OH + isoprene reaction intermediate using ab initio molecular dynamics.

    Science.gov (United States)

    Dietrick, Scott M; Pacheco, Alexander B; Phatak, Prasad; Stevens, Philip S; Iyengar, Srinivasan S

    2012-01-12

    The effect of water on the stability and vibrational states of a hydroxy-isoprene adduct is probed through the introduction of 1-15 water molecules. It is found that when a static nuclear harmonic approximation is invoked there is a substantial red-shift of the alcohol O-H stretch (of the order of 800 cm(-1)) as a result of introduction of water. When potential energy surface sampling and associated anharmonicities are introduced through finite temperature ab initio dynamics, this hydroxy-isoprene OH stretch strongly couples with all the water vibrational modes as well as the hydroxy-isoprene OH bend modes. A new computational technique is introduced to probe the coupling between these modes. The method involves a two-dimensional, time-frequency analysis of the finite temperature vibrational properties. Such an analysis not only provides information about the modes that are coupled as a result of finite-temperature analysis, but also the temporal evolution of such coupling.

  2. In-Medium Pion Valence Distribution Amplitude

    CERN Document Server

    Tsushima, K

    2016-01-01

    After a brief review of the quark-based model for nuclear matter, and some pion properties in medium presented in our previous works, we report new results for the pion valence wave function as well as the valence distribution amplitude in medium, which are presented in our recent article. We find that both the in-medium pion valence distribution and the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.

  3. In-Medium Pion Valence Distribution Amplitude

    Science.gov (United States)

    Tsushima, K.; de Melo, J. P. B. C.

    2017-03-01

    After a brief review of the quark-based model for nuclear matter, and some pion properties in medium presented in our previous works, we report new results for the pion valence wave function as well as the valence distribution amplitude in medium, which are presented in our recent article. We find that both the in-medium pion valence distribution and the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.

  4. Effects of Li and Na intercalation on electronic, bonding and thermoelectric transport properties of MX{sub 2} (M = Ta; X = S or Se) dichalcogenides – Ab initio investigation

    Energy Technology Data Exchange (ETDEWEB)

    Meziane, Souheyr; Feraoun, Houda [Unité de Recherche Matériaux et Energies Renouvelables – URMER, Université de Tlemcen (Algeria); Ouahrani, Tarik [Laboratoire de Physique Théorique, Ecole Préparatoire en Sciences et Techniques, B.P. 230, 13000 Tlemcen (Algeria); Esling, Claude, E-mail: claude.esling@univ-lorraine.fr [Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux, LEM3 UMR CNRS 7239, Université de Lorraine UL, Metz 57045 (France); Laboratoire d’Excellence “DAMAS”: Design of Metal Alloys for low-mAss Structures, Université de Lorraine – Metz, Ile du Saulcy, 57045 Metz Cedex 01 (France)

    2013-12-25

    Highlights: •Topological method is used to analyze the chemical bonding in Li(Na)TaX{sub 2} dichalcogenide compounds. •For the first time, Seebeck coefficient, electrical resistivity and thermal conductivity were estimated. •The best figure of merit is established for 2H-LiTaS{sub 2}. •Some new thermoelectric compounds are found. -- Abstract: Using the pseudo-potential method and semi-classical Boltzmann theory, electronic, chemical bonding and thermoelectric transport properties of sample and Li or Na intercalated Ta(S, Se){sub 2} dichalcogenides have been reported. The chemical bonding is studied using the Quantum Theory of Atoms in Molecules (QTAIM). Then, the Seebeck coefficient, electrical resistivity, electrical conductivity, thermal conductivity and figure of merit have been calculated in the temperature range 100–700 K. It was shown that the thermoelectric transport properties strongly depend on the Alkali metals doping and the two main structures 1T- or 2H- as well as the temperature. 2H-LiTaS{sub 2} have been selected as the best candidate for thermoelectrical applications with zT = 1.1.

  5. Ab initio investigations of the electronic structures and chemical bonding in LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Matar, Samir F. [CNRS, ICMCB, UPR 9048, F‐33600 Pessac (France); Université de Bordeaux, ICMCB, UPR 9048, F‐33600 Pessac (France); Al-Alam, Adel; Ouaini, Naïm [Université Saint-Esprit de Kaslik (USEK), Groupe OCM (Optimization et Caractérisation des Matériaux), CSR-USEK, CNRS-L, Jounieh (Lebanon); Pöttgen, Rainer, E-mail: pottgen@uni-muenster.de [Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstraße 30, D-48149 Münster (Germany)

    2013-06-15

    The electronic structures of the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7} were studied by DFT calculations. Both phosphides consist of three-dimensional [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] polyanionic networks which leave hexagonal channels for the lithium atoms. COOP data show strong Co–P and Co–Co bonding within the polyanions. The lithium atoms have trigonal prismatic phosphorus coordination. Total energy calculations indicate stability upon de-lithiation towards the Co{sub 6}P{sub 4} and Co{sub 12}P{sub 7} substructures - Graphical abstract: The cobalt–phosphorus networks in LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. - Highlights: • Chemical bonding resolved in the metal-rich phosphides LiCo{sub 6}P{sub 4} and Li{sub 2}Co{sub 12}P{sub 7}. • Strong covalent Co–P bonding character in the [Co{sub 6}P{sub 4}] and [Co{sub 12}P{sub 7}] substructures. • Total energy calculations indicate stability of the de-lithiated substructures.

  6. Boryl substitution of acetaldehyde makes it an enol: inconsistency between Gn/CBS and ab initio/DFT data.

    Science.gov (United States)

    Balabin, Roman M

    2010-03-18

    Tautomerism, a particular case of isomerism, plays an important role in modern organic chemistry, biochemistry, medicinal chemistry, pharmacology, and molecular biology. Inconsistency between results of complex energy computation methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio/DFT ones (CCSD(T)/CBS, MP2/CBS, and B3LYP/aug-cc-pVTZ) is found. Gn/CBS methods provide a qualitatively different description of tautomeric (keto-enol) equilibrium in 2-substituted acetaldehydes. According to valence focal point analysis (FPA) based on CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z energies, boryl substitution of acetaldehyde makes it an enol. In other words, enol was found to be the global minimum on the potential energy surface (PES) of C(2)H(5)BO. Gn/CBS methods predict the keto form to be the minimum. The relative energy of alkenol, CH(BH(2))=CH(OH), is calculated to be -1.67 +/- 0.82 kcal mol(-1) at CCSD(T)/CBS level of theory. Hydrogen shift effects are also calculated in two other 2-substituted acetaldehydes, namely, 3-oxopropanenitrile (C(3)H(3)NO) and ethanal (C(2)H(4)O), with a general formula of XH(2)C-CHO (X = BH(2), CN, and H). Electron density (charge) transfer between the C=C double bond and the free p orbital of the boron atom (B) in a boryl group (BH(2)) greatly stabilizes enol with respect to ketone, CH(2)(BH(2))-CHO. The first known stabilization of enol in an acetaldehyde derivative, without an intramolecular hydrogen bond (H-bond), questions the accuracy of complex energy computation methods for boron-containing molecules. The possible reasons and consequences of this finding are discussed.

  7. Ab initio molecular dynamics simulations of the Li4F4 cluster

    Science.gov (United States)

    Heidenreich, A.; Sauer, J.

    1995-12-01

    Molecular dynamics simulations have been performed directly on the ab initio potential energy surface of Li4F4, which was generated within the Hartree-Fock approximation using a Gaussian basis set (split valence contraction). Trajectories at different temperatures yield the temperature dependence of the infrared spectra and the photoelectron spectra. For the infrared spectra comparison is made with MD results using a shell model ion pair potential function.

  8. Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

    Science.gov (United States)

    Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

    2007-02-05

    The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42

  9. The Pauling 3-Electron Bond: A Recommendation for the Use of the Linnett Structure.

    Science.gov (United States)

    Harcourt, Richard D.

    1985-01-01

    Recommends the Linnett structure IV (as in VIII for molecular oxygen) for future use when a valence-bond structure for a Pauling 3-electron bond is required. Examples are provided to illustrate why this recommendation is made. (JN)

  10. Ab initio Molecular Dynamics Study on Small Carbon Nanotubes

    Institute of Scientific and Technical Information of China (English)

    叶林晖; 刘邦贵; 王鼎盛

    2001-01-01

    Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag and armchair nanotubes there are two nonequivalent bond lengths. One bond stretches from that of the graphene sheet, while the other shrinks. Small variations on bond angles are also shown. Energy bands are calculated for the optimized structures. It is found that the intrinsic curvature of the very small nanotube greatly modifies the energy band which can no longer be well described in the tight-binding zone-folding picture. In our calculation very small nanotubes are metallic. The energy per atom fits quite well with the relation of E(R) = E0 + f/R2 even for the extreme small radius. The implications of the results on the properties of small nanotubes are discussed.

  11. Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations

    Science.gov (United States)

    Good, Brian S.

    2004-01-01

    We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.

  12. Exploring the properties of valence electron based potential functions for the nonbonded interactions in atomistic force fields

    CERN Document Server

    Plattner, Nuria

    2016-01-01

    The possibility to construct and parametrize the nonbonded interactions in atomistic force fields based on the valence electron structure of molecules is explored in this paper. Three different charge distribution models using simple valence electron based potential functions are introduced and compared. It is shown that the three models can be constructed such that they only require one adjustable parameter for the electrostatic potential of a molecule. The accuracy of the electrostatic potential is evaluated for the three models and compared to population-derived charges and higher order multipole moments for a set of 12 small molecules. Furthermore the accuracy and parametrization of the interaction energies of the three models is evaluated based on {\\it ab initio} intermolecular interaction energies. It is shown that the valence electron potential models provide systematic advantages over conventional point charge models for the calculation of intermolecular interaction energies even with the very simple ...

  13. Effects of Nb and Si on densities of valence electrons in bulk and defects of Fe3Al alloys

    Institute of Scientific and Technical Information of China (English)

    邓文; 钟夏平; 黄宇阳; 熊良钺; 王淑荷; 郭建亭; 龙期威

    1999-01-01

    Positron lifetime measurements have been performed in binary Fe3Al and Fe3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe3Al alloy. It indicates that, the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds with Al atoms, and the bonding nature in Fe3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic bonding cohesion. This makes the alloy more brittle. The addition of Nb to Fe3Al results in the decrease of the ordering energy of the alloy and increases the density of valence electron and th

  14. Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols

    Directory of Open Access Journals (Sweden)

    Stefanie Krysiak

    2015-05-01

    Full Text Available Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM. The comparison of single catechols (dopamine with multiple catechols on hyperbranched polyglycerols (hPG at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings.

  15. Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols.

    Science.gov (United States)

    Krysiak, Stefanie; Wei, Qiang; Rischka, Klaus; Hartwig, Andreas; Haag, Rainer; Hugel, Thorsten

    2015-01-01

    Nature often serves as a model system for developing new adhesives. In aqueous environments, mussel-inspired adhesives are promising candidates. Understanding the mechanism of the extraordinarily strong adhesive bonds of the catechol group will likely aid in the development of adhesives. With this aim, we study the adhesion of catechol-based adhesives to metal oxides on the molecular level using atomic force microscopy (AFM). The comparison of single catechols (dopamine) with multiple catechols on hyperbranched polyglycerols (hPG) at various pH and dwell times allowed us to further increase our understanding. In particular, we were able to elucidate how to achieve strong bonds of different valency. It was concluded that hyperbranched polyglycerols with added catechol end groups are promising candidates for durable surface coatings.

  16. Hydrogen Bonding to Alkanes: Computational Evidence

    DEFF Research Database (Denmark)

    Hammerum, Steen; Olesen, Solveig Gaarn

    2009-01-01

    The structural, vibrational, and energetic properties of adducts of alkanes and strong cationic proton donors were studied with composite ab initio calculations. Hydrogen bonding in [D-H+ H-alkyl] adducts contributes to a significant degree to the interactions between the two components, which...... is substantiated by NBO and AIM results. The hydrogen bonds manifest themselves in the same manner as conventional hydrogen bonds, D-H bond elongation, D-H vibrational stretching frequency red shift and intensity increase, and adduct stabilization. The alkane adducts also exhibit elongation of the C-H bonds...

  17. Thermochemical data for CVD modeling from ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Ho, P. [Sandia National Labs., Albuquerque, NM (United States); Melius, C.F. [Sandia National Labs., Livermore, CA (United States)

    1993-12-31

    Ab initio electronic-structure calculations are combined with empirical bond-additivity corrections to yield thermochemical properties of gas-phase molecules. A self-consistent set of heats of formation for molecules in the Si-H, Si-H-Cl, Si-H-F, Si-N-H and Si-N-H-F systems is presented, along with preliminary values for some Si-O-C-H species.

  18. Fundamental aspects of recoupled pair bonds. I. Recoupled pair bonds in carbon and sulfur monofluoride

    Energy Technology Data Exchange (ETDEWEB)

    Dunning, Thom H., E-mail: thdjr@uw.edu; Xu, Lu T.; Takeshita, Tyler Y. [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois 61801 (United States)

    2015-01-21

    The number of singly occupied orbitals in the ground-state atomic configuration of an element defines its nominal valence. For carbon and sulfur, with two singly occupied orbitals in their {sup 3}P ground states, the nominal valence is two. However, in both cases, it is possible to form more bonds than indicated by the nominal valence—up to four bonds for carbon and six bonds for sulfur. In carbon, the electrons in the 2s lone pair can participate in bonding, and in sulfur the electrons in both the 3p and 3s lone pairs can participate. Carbon 2s and sulfur 3p recoupled pair bonds are the basis for the tetravalence of carbon and sulfur, and 3s recoupled pair bonds enable sulfur to be hexavalent. In this paper, we report generalized valence bond as well as more accurate calculations on the a{sup 4}Σ{sup −} states of CF and SF, which are archetypal examples of molecules that possess recoupled pair bonds. These calculations provide insights into the fundamental nature of recoupled pair bonds and illustrate the key differences between recoupled pair bonds formed with the 2s lone pair of carbon, as a representative of the early p-block elements, and recoupled pair bonds formed with the 3p lone pair of sulfur, as a representative of the late p-block elements.

  19. Ionic bonding of lanthanides, as influenced by d- and f-atomic orbitals, by core-shells and by relativity.

    Science.gov (United States)

    Ji, Wen-Xin; Xu, Wei; Schwarz, W H Eugen; Wang, Shu-Guang

    2015-03-15

    Lanthanide trihalide molecules LnX3 (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO-coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen-core approximations for Lu were compared: the (1s(2) -4d(10) ) [Pd] medium core, the [Pd+5s(2) 5p(6) = Xe] and [Pd+4f(14) ] large cores, and the [Pd+4f(14) +5s(2) 5p(6) ] very large core. The errors of LuX bonding are more serious on freezing the 5p(6) shell than the 4f(14) shell, more serious upon core-freezing than on the effective-core-potential approximation. The LnX distances correlate linearly with the AO radii of the ionic outer shells, Ln(3+) -5p(6) and X(-) -np(6) , characteristic for dominantly ionic Ln(3+) -X(-) binding. The heavier halogen atoms also bind covalently with the Ln-5d shell. Scalar relativistic effects contract and destabilize the LuX bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length Re , bond force k, and bond stretching frequency vs do not follow the simple rules of Badger and Gordy (Re ∼BE∼k∼vs ). The so-called degeneracy-driven covalence, meaning strong mixing of accidentally near-degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.

  20. Definition and Application of Topological Index Based on Bond Connectivity

    Institute of Scientific and Technical Information of China (English)

    WANG Zhen-dong; YANG Feng; YANG Hai-lang; LUO Ming-dao; QU Song-sheng

    2003-01-01

    Bond connectivity topological index Si based on chemical bonds was defined by using a matrix method.And Si is formed by atomic parameters such as the number of valence electrons,the number of the highest main quantum of atoms and the bonding electrons and bond parameters such as the length of bonds,the electronegativity difference of bonding atoms.The molecular bond connectivity topological index S is composed of Si.The thermodynamic properties of saturated hydrocarbons,unsaturated hydrocarbons,oxygen organic,methane halide and transitional element compounds and the molecular bond connectivity topological index S have an optimal correlative relationship.

  1. Valence electron structure of cast iron and graphltization behaviour criterion of elements

    Institute of Scientific and Technical Information of China (English)

    刘志林; 李志林; 孙振国; 杨晓平; 陈敏

    1995-01-01

    The valence electron structure of common alloy elements in phases of cast iron is calculated- The relationship between the electron structure of alloy elements and equilibrium, non-equilibrium solidification and graphitization is revealed by defining the bond energy of the strongest bond in a phase as structure formation factor S. A criterion of graphitization behaviour of elements is advanced with the critical value of the structure formation factor of graphite and the n of the strongest covalent bond in cementite. It is found that this theory conforms to practice very well when the criterion is applied to the common alloy elements.

  2. Infinite-basis calculations of binding energies for the hydrogen bonded and stacked tetramers of formic acid and formamide and their use for validation of hybrid DFT and ab initio methods.

    Science.gov (United States)

    Zhao, Yan; Truhlar, Donald G

    2005-08-04

    Benchmark stabilization energies for planar H-bonded and stacked structures of formic acid tetramers and formamide tetramers were determined as the sum of the infinite basis set limit of MP2 energies and a CCSD(T) correction term evaluated with the 6-31G*(0.25) basis set. The infinite basis (IB) set limit of MP2 energies was determined by two-point extrapolation using the aug-cc-pVXZ basis sets for X = D and T and separate extrapolation of the Hartree-Fock and correlation energies with new IB parameters for augmented basis sets determined here. Final stabilization energies (kcal/mol) for the tetramer studied are in the range of 4.6 to approximately 6.7 kcal/mol and they were used as reference data to test 14 density functionals. Among the tested DFT methods, PWB6K gives the best performance with an average error equal to only 30% of the average binding energy. In contrast, the popular B3LYP functional has an average error of 85%. We recommend the PWB6K method for exploring the potential energy surfaces of organic complexes and clusters and supramolecular assemblies.

  3. Hydrogen bonds of 2-aminothiazoles in intermolecular complexes (1:1 and 1:2) with proton acceptors in solutions

    Science.gov (United States)

    Borisenko, V. E.; Koll, A.; Kolmakov, E. E.; Rjasnyi, A. G.

    2006-02-01

    ) were determined. The correlations were stated between spectral, geometrical, force and electro optic parameters of free and bonded molecules. In the approximation of DFT-B3LYP/6-31G** and ab initio MP2/6-31G**, the atom charge distribution (according to Mulliken), geometrical and force characteristics and dipole moments μ0 of 2-aminothiazoles were calculated. The quantum mechanical calculations, valence force field calculations and the experimental results were shown to be in good agreement.

  4. Development of Remote Plutonium Valence State Analyzer

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    <正>In the Purex process of spent fuel reprocessing, the separation of uranium and plutonium depends on the capability extracting state plutonium ions with various valence by TBP. The separate degree of

  5. Modelling the local atomic structure of molybdenum in nuclear waste glasses with ab initio molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    None, None

    2016-01-01

    The nature of chemical bonding of molybdenum in high level nuclear waste glasses has been elucidated by ab initio molecular dynamics simulations. Two compositions, (SiO2)57.5 – (B2O3)10 – (Na2O)15 – (CaO)15 – (MoO3)2.5 and (SiO2)57.3 – (B2O3)20 – (Na2O)6.8 – (Li2O)13.4 – (MoO3)2.5 , were considered in order to investigate the effect of ionic and covalent components on the glass structure and the formation of the crystallisation precursors (Na2MoO4 and CaMoO4). The coordination environments of Mo cations and the corresponding bond lengths calculated from our model are in excellent agreement with experimental observations. The analysis of the first coordination shell reveals two different types of molybdenum host matrix bonds in the lithium sodium borosilicate glass. Based on the structural data and the bond valence model, we demonstrate that the Mo cation can be found in a redox state and the molybdate tetrahedron can be connected with the borosilicate network in a way that inhibits the formation of crystalline molybdates. These results significantly extend our understanding of bonding in Mo-containing nuclear waste glasses and demonstrate that tailoring the glass composition to specific heavy metal constituents can facilitate incorporation of heavy metals at high concentrations. K.K. was supported through the Impact Studentship scheme at UCL co-funded by the IHI Corporation and UCL. P.V.S. thanks the Royal Society, which supported preliminary work on this project, and the Laboratory Directed Research and Development program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk).

  6. An investigation of ab initio shell-model interactions derived by no-core shell model

    Science.gov (United States)

    Wang, XiaoBao; Dong, GuoXiang; Li, QingFeng; Shen, CaiWan; Yu, ShaoYing

    2016-09-01

    The microscopic shell-model effective interactions are mainly based on the many-body perturbation theory (MBPT), the first work of which can be traced to Brown and Kuo's first attempt in 1966, derived from the Hamada-Johnston nucleon-nucleon potential. However, the convergence of the MBPT is still unclear. On the other hand, ab initio theories, such as Green's function Monte Carlo (GFMC), no-core shell model (NCSM), and coupled-cluster theory with single and double excitations (CCSD), have made many progress in recent years. However, due to the increasing demanding of computing resources, these ab initio applications are usually limited to nuclei with mass up to A = 16. Recently, people have realized the ab initio construction of valence-space effective interactions, which is obtained through a second-time renormalization, or to be more exactly, projecting the full-manybody Hamiltonian into core, one-body, and two-body cluster parts. In this paper, we present the investigation of such ab initio shell-model interactions, by the recent derived sd-shell effective interactions based on effective J-matrix Inverse Scattering Potential (JISP) and chiral effective-field theory (EFT) through NCSM. In this work, we have seen the similarity between the ab initio shellmodel interactions and the interactions obtained by MBPT or by empirical fitting. Without the inclusion of three-body (3-bd) force, the ab initio shell-model interactions still share similar defects with the microscopic interactions by MBPT, i.e., T = 1 channel is more attractive while T = 0 channel is more repulsive than empirical interactions. The progress to include more many-body correlations and 3-bd force is still badly needed, to see whether such efforts of ab initio shell-model interactions can reach similar precision as the interactions fitted to experimental data.

  7. A Corpuscular Picture of Electrons in Chemical Bond

    CERN Document Server

    Ando, Koji

    2015-01-01

    We introduce a theory of chemical bond with a corpuscular picture of electrons. It employs a minimal set of localized electron wave packets with 'floating and breathing' degrees of freedom and the spin-coupling of non-orthogonal valence-bond theory. It accurately describes chemical bonds in ground and excited states of spin singlet and triplet, in a distinct manner from conventional theories, indicating potential for establishing a dynamical theory of electrons in chemical bonds.

  8. Hydrogen bonding in tight environments

    DEFF Research Database (Denmark)

    Pirrotta, Alessandro; Solomon, Gemma C.; Franco, Ignacio

    2016-01-01

    The single-molecule force spectroscopy of a prototypical class of hydrogen-bonded complexes is computationally investigated. The complexes consist of derivatives of a barbituric acid and a Hamilton receptor that can form up to six simultaneous hydrogen bonds. The force-extension (F-L) isotherms...... of the host-guest complexes are simulated using classical molecular dynamics and the MM3 force field, for which a refined set of hydrogen bond parameters was developed from MP2 ab initio computations. The F-L curves exhibit peaks that signal conformational changes during elongation, the most prominent...... of which is in the 60-180 pN range and corresponds to the force required to break the hydrogen bonds. These peaks in the F-L curves are shown to be sensitive to relatively small changes in the chemical structure of the host molecule. Thermodynamic insights into the supramolecular assembly were obtained...

  9. Nature of the Frequency Shift of Hydrogen Valence Vibrations

    CERN Document Server

    Zhyganiuk, I V

    2015-01-01

    The physical nature of a frequency shift of hydrogen valence vibrations in a water molecule due to its interaction with neighbor molecules has been studied. Electrostatic forces connected with the multipole moments of molecules are supposed to give a dominating contribution to the intermolecular interaction. The frequency shift was calculated in the case where two neighbor molecules form a dimer. The obtained result is in qualitative agreement with the frequency shifts observed for water vapor, hexagonal ice, and liquid water, as well as for aqueous solutions of alcohols. This fact testifies to the electrostatic nature of H-bonds used to describe both the specific features of the intermolecular interaction in water and the macroscopic properties of the latter.

  10. Phonocatalysis. An ab initio simulation experiment

    Directory of Open Access Journals (Sweden)

    Kwangnam Kim

    2016-06-01

    Full Text Available Using simulations, we postulate and show that heterocatalysis on large-bandgap semiconductors can be controlled by substrate phonons, i.e., phonocatalysis. With ab initio calculations, including molecular dynamic simulations, the chemisorbed dissociation of XeF6 on h-BN surface leads to formation of XeF4 and two surface F/h-BN bonds. The reaction pathway and energies are evaluated, and the sorption and reaction emitted/absorbed phonons are identified through spectral analysis of the surface atomic motion. Due to large bandgap, the atomic vibration (phonon energy transfer channels dominate and among them is the match between the F/h-BN covalent bond stretching and the optical phonons. We show that the chemisorbed dissociation (the pathway activation ascent requires absorption of large-energy optical phonons. Then using progressively heavier isotopes of B and N atoms, we show that limiting these high-energy optical phonons inhibits the chemisorbed dissociation, i.e., controllable phonocatalysis.

  11. Strong influence of coadsorbate interaction on CO desorption dynamics on Ru(0001) probed by ultrafast x-ray spectroscopy and ab initio simulations

    Energy Technology Data Exchange (ETDEWEB)

    Xin, H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); LaRue, J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Oberg, H. [Stockholm Univ., Stockholm (Sweden); Beye, M. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Helmholtz Zentrum Berlin fur Materialien und Energie GmbH, Berlin (Germany); Dell' Angela, M. [Univ. of Hamburg and Center for Free Electron Laser Science, Hamburg (Germany); Turner, J. J. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Gladh, J. [Stockholm Univ., Stockholm (Sweden); Ng, M. L. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Sellberg, J. A. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Helmholtz Zentrum Berlin fur Materialien und Energie GmbH, Berlin (Germany); Kaya, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Mercurio, G. [Univ. of Hamburg and Center for Free Electron Laser Science, Hamburg (Germany); Hieke, F. [Univ. of Hamburg and Center for Free Electron Laser Science, Hamburg (Germany); Nordlund, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Schlotter, W. F. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Dakovski, G. L. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Minitti, M. P. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Fohlisch, A. [Helmholtz Zentrum Berlin fur Materialien und Energie GmbH, Berlin (Germany); Univ. Potsdam, Potsdam (Germany); Wolf, M. [Fritz-Haber Institute of the Max-Planck-Society, Berlin (Germany); Wurth, W. [Univ. of Hamburg and Center for Free Electron Laser Science, Hamburg (Germany); DESY Photon Science, Hamburg (Germany); Ogasawara, H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Norskov, J. K. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Ostrom, H. [Stockholm Univ., Stockholm (Sweden); Pettersson, L. G. M. [Stockholm Univ., Stockholm (Sweden); Nilsson, A. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stockholm Univ., Stockholm (Sweden); Ablid-Pedersen, F. [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2015-04-16

    We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5σ and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.

  12. Structural and dynamical aspects of the unsymmetric hydration of Sb(III): an ab initio quantum mechanical charge field molecular dynamics simulation.

    Science.gov (United States)

    Lim, Len Herald V; Bhattacharjee, Anirban; Asam, S Sikander; Hofer, Thomas S; Randolf, Bernhard R; Rode, Bernd M

    2010-03-01

    An ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation was performed to investigate the behavior of the Sb(3+) ion in aqueous solution. The simulation reveals a significant influence of the residual valence shell electron density on the solvation structure and dynamics of Sb(3+). A strong hemidirectional behavior of the ligand binding pattern is observed for the first hydration shell extending up to the second hydration layer. The apparent domain partitioned structural behavior was probed by solvent reorientational kinetics and three-body distribution functions. The three-dimensional hydration space was conveniently segmented such that domains having different properties were properly resolved. The approach afforded a fair isolation of localized solvent structural and dynamical motifs that Sb(3+) seems to induce to a remarkable degree. Most intriguing is the apparent impact of the lone pair electrons on the second hydration shell, which offers insight into the mechanistic aspects of hydrogen bonding networks in water. Such electronic effects observed in the hydration of Sb(3+) can only be studied by applying a suitable quantum mechanical treatment including first and second hydration shell as provided by the QMCF ansatz.

  13. Introducing Students to Inner Sphere Electron Transfer Concepts through Electrochemistry Studies in Diferrocene Mixed-Valence Systems

    Science.gov (United States)

    Ventura, Karen; Smith, Mark B.; Prat, Jacob R.; Echegoyen, Lourdes E.; Villagran´, Dino

    2017-01-01

    We have designed a 4 h physical chemistry laboratory to introduce upper division students to electrochemistry concepts, including mixed valency and electron transfer (ET), using cyclic and differential pulse voltammetries. In this laboratory practice, students use a ferrocene dimer consisting of two ferrocene centers covalently bonded through a…

  14. Valence electron structure analysis of refining mecha-nism of Sc and Ti additions on aluminum

    Institute of Scientific and Technical Information of China (English)

    LI PieJie; YE YiCong; HE LiangJu

    2009-01-01

    The mechanism of the difference of refining effect between Sc and Ti adding to aluminum can not be explained substantially with traditional theory. Valence electron structures of AI-Ti and Al-Sc alloys have been studied by using the empirical electron theory of solids and molecules (EET). The covalent bond electron numbers and interfacial electron density differences are calculated. The conclusion is that, in the two alloys, different covalent bond electron numbers of nucleation particles, and different electron densities on the interface between the second phase particles and the matrix, fundamentally lead to the difference of refining effect between Sc and Ti adding to aluminum.

  15. Affective Priming with Associatively Acquired Valence

    Science.gov (United States)

    Aguado, Luis; Pierna, Manuel; Saugar, Cristina

    2005-01-01

    Three experiments explored the effect of affectively congruent or incongruent primes on evaluation responses to positive or negative valenced targets (the "affective priming" effect). Experiment 1 replicated the basic affective priming effect with Spanish nouns: reaction time for evaluative responses (pleasant/unpleasant) were slower on…

  16. Emotional valence categorization using holistic image features

    NARCIS (Netherlands)

    Yanulevskaya, V.; van Gemert, J.C.; Roth, K.; Herbold, A.K.; Sebe, N.; Geusebroek, J.M.

    2008-01-01

    Can a machine learn to perceive emotions as evoked by an artwork? Here we propose an emotion categorization system, trained by ground truth from psychology studies. The training data contains emotional valences scored by human subjects on the International Affective Picture System (IAPS), a standard

  17. Masked emotional priming beyond global valence activations

    NARCIS (Netherlands)

    Rohr, M.; Degner, J.; Wentura, D.

    2012-01-01

    An immense body of research demonstrates that emotional facial expressions can be processed unconsciously. However, it has been assumed that such processing takes place solely on a global valence-based level, allowing individuals to disentangle positive from negative emotions but not the specific em

  18. Liquid Be, Ca and Ba. An orbital-free ab-initio molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Rio, B. G. del; González, L. E. [Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011 Valladolid (Spain)

    2015-08-17

    Several static and dynamic properties of liquid beryllium (l-Be), liquid calcium (l-Ca) and liquid barium (l-Ba) near their triple point have been evaluated by the orbital-free ab initio molecular dynamics method (OF-AIMD), where the interaction between valence electrons and ions is described by means of local pseudopotentials. These local pseudopotentials used were constructed through a force-matching process with those obtained from a Kohn-Sham ab initio molecular dynamics study (KS-AIMD) of a reduced system with non-local pseudopotentials. The calculated static structures show good agreement with the available experimental data, including an asymmetric second peak in the structure factor which has been linked to the existence of a marked icosahedral short-range order in the liquid. As for the dynamic properties, we obtain collective density excitations whose associated dispersion relations exhibit a positive dispersion.

  19. Valence atom with bohmian quantum potential: the golden ratio approach

    Directory of Open Access Journals (Sweden)

    Putz Mihai V

    2012-11-01

    Full Text Available Abstract Background The alternative quantum mechanical description of total energy given by Bohmian theory was merged with the concept of the golden ratio and its appearance as the Heisenberg imbalance to provide a new density-based description of the valence atomic state and reactivity charge with the aim of clarifying their features with respect to the so-called DFT ground state and critical charge, respectively. Results The results, based on the so-called double variational algorithm for chemical spaces of reactivity, are fundamental and, among other issues regarding chemical bonding, solve the existing paradox of using a cubic parabola to describe a quadratic charge dependency. Conclusions Overall, the paper provides a qualitative-quantitative explanation of chemical reactivity based on more than half of an electronic pair in bonding, and provide new, more realistic values for the so-called “universal” electronegativity and chemical hardness of atomic systems engaged in reactivity (analogous to the atoms-in-molecules framework.

  20. Ab initio adiabatic and quasidiabatic potential energy surfaces of H++ CN system

    Indian Academy of Sciences (India)

    Bhargava Anusuri; Sanjay Kumar

    2016-02-01

    We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H++ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials.

  1. Valence-Dependent Belief Updating: Computational Validation.

    Science.gov (United States)

    Kuzmanovic, Bojana; Rigoux, Lionel

    2017-01-01

    People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates) with trials with bad news (worse-than-expected base rates). After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic) Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational) Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on reinforcement

  2. Valence-Dependent Belief Updating: Computational Validation

    Directory of Open Access Journals (Sweden)

    Bojana Kuzmanovic

    2017-06-01

    Full Text Available People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates with trials with bad news (worse-than-expected base rates. After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on

  3. Ab initio molecular dynamics of solvation effects on reactivity at electrified interfaces

    Science.gov (United States)

    Herron, Jeffrey A.; Morikawa, Yoshitada; Mavrikakis, Manos

    2016-08-01

    Using ab initio molecular dynamics as implemented in periodic, self-consistent (generalized gradient approximation Perdew-Burke-Ernzerhof) density functional theory, we investigated the mechanism of methanol electrooxidation on Pt(111). We investigated the role of water solvation and electrode potential on the energetics of the first proton transfer step, methanol electrooxidation to methoxy (CH3O) or hydroxymethyl (CH2OH). The results show that solvation weakens the adsorption of methoxy to uncharged Pt(111), whereas the binding energies of methanol and hydroxymethyl are not significantly affected. The free energies of activation for breaking the C-H and O-H bonds in methanol were calculated through a Blue Moon Ensemble using constrained ab initio molecular dynamics. Calculated barriers for these elementary steps on unsolvated, uncharged Pt(111) are similar to results for climbing-image nudged elastic band calculations from the literature. Water solvation reduces the barriers for both C-H and O-H bond activation steps with respect to their vapor-phase values, although the effect is more pronounced for C-H bond activation, due to less disruption of the hydrogen bond network. The calculated activation energy barriers show that breaking the C-H bond of methanol is more facile than the O-H bond on solvated negatively biased or uncharged Pt(111). However, with positive bias, O-H bond activation is enhanced, becoming slightly more facile than C-H bond activation.

  4. Geometry of the valence transition induced surface reconstruction of Sm(0001)

    CERN Document Server

    Lundgren, E; Nyholm, R; Torrelles, X; Rius, J; Delin, A; Grechnev, A; Eriksson, O; Konvicka, C; Schmid, M; Varga, P

    2002-01-01

    We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and {\\it ab initio} calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the $4f$ electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.

  5. Coronal lines and the importance of deep core-valence correlation in Ag-like ions

    CERN Document Server

    Grumer, Jon; Brage, Tomas; Li, Wenxian; Huldt, Sven; Hutton, Roger; Zou, Yaming

    2014-01-01

    We report on large-scale and critically evaluated {\\em ab initio} MCDHF calculations of the wavelength of the "coronal", M1 transition $4f\\ ^2\\mathrm{F}_{5/2}^o~-~^2\\mathrm{F}_{7/2}^o$ in Ag-like ions. The transition between these two fine structure levels, which makes up the ground term for $Z \\ge 62$ in the isoelectronic sequence, has recently been observed in Yb$^{23+}$ and W$^{27+}$, where the latter could be of great importance for fusion plasma diagnostics. We present recommended values for all members of the sequence between $Z = 50$ and $94$, which are supported by excellent agreement with values from recent experiments. The importance of including core-valence correlation with the $n=3$ shell in the theoretical model is emphasized. The results show close to spectroscopic accuracy for these forbidden lines.

  6. Physical Nature of Hydrogen Bond

    CERN Document Server

    Zhyganiuk, I V

    2015-01-01

    The physical nature and the correct definition of hydrogen bond (H-bond) are considered.\\,\\,The influence of H-bonds on the thermodynamic, kinetic, and spectroscopic properties of water is analyzed.\\,\\,The conventional model of H-bonds as sharply directed and saturated bridges between water molecules is incompatible with the behavior of the specific volume, evaporation heat, and self-diffusion and kinematic shear viscosity coefficients of water. On the other hand, it is shown that the variation of the dipole moment of a water molecule and the frequency shift of valence vibrations of a hydroxyl group can be totally explained in the framework of the electrostatic model of H-bond.\\,\\,At the same time, the temperature dependences of the heat capacity of water in the liquid and vapor states clearly testify to the existence of weak H-bonds.\\,\\,The analysis of a water dimer shows that the contribution of weak H-bonds to its ground state energy is approximately 4--5 times lower in comparison with the energy of electr...

  7. Entropically patchy particles: engineering valence through shape entropy.

    Science.gov (United States)

    van Anders, Greg; Ahmed, N Khalid; Smith, Ross; Engel, Michael; Glotzer, Sharon C

    2014-01-28

    Patchy particles are a popular paradigm for the design and synthesis of nanoparticles and colloids for self-assembly. In "traditional" patchy particles, anisotropic interactions arising from patterned coatings, functionalized molecules, DNA, and other enthalpic means create the possibility for directional binding of particles into higher-ordered structures. Although the anisotropic geometry of nonspherical particles contributes to the interaction patchiness through van der Waals, electrostatic, and other interactions, how particle shape contributes entropically to self-assembly is only now beginning to be understood. The directional nature of entropic forces has recently been elucidated. A recently proposed theoretical framework that defines and quantifies directional entropic forces demonstrates the anisotropic-that is, patchy-nature of these emergent, attractive forces. Here we introduce the notion of entropically patchy particles as the entropic counterpart to enthalpically patchy particles. Using three example "families" of shapes, we show how to modify entropic patchiness by introducing geometric features to the particles via shape operations so as to target specific crystal structures assembled here with Monte Carlo simulations. We quantify the emergent entropic valence via a potential of mean force and torque. We show that these forces are on the order of a few kBT at intermediate densities below the onset of crystallization. We generalize these shape operations to shape anisotropy dimensions, in analogy with the anisotropy dimensions introduced for enthalpically patchy particles. Our findings demonstrate that entropic patchiness and emergent valence provide a way of engineering directional bonding into nanoparticle systems, whether in the presence or absence of additional, non-entropic forces.

  8. The electronic structure and chemical bonding of vitamin B12

    Science.gov (United States)

    Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.

    2003-05-01

    The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.

  9. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon Čopar

    2014-05-01

    Full Text Available Generalized Janus nematic colloids based on various morphologies of particle surface patches imposing homeotropic and planar surface anchoring are demonstrated. By using mesoscopic numerical modeling, multiple types of Janus particles are explored, demonstrating a variety of novel complex colloidal structures. We also show binding of Janus particles to a fixed Janus post in the nematic cell, which acts as a seed and a micro-anchor for the colloidal structure. Janus colloidal structures reveal diverse topological defect configurations, which are effectively combinations of surface boojum and bulk defects. Topological analysis is applied to defects, importantly showing that topological charge is not a well determined topological invariant in such patchy nematic Janus colloids. Finally, this work demonstrates colloidal structures with designable valence, which could allow for targeted and valence-conditioned self-assembly at micro- and nano-scale.

  10. Evaluative conditioning induces changes in sound valence

    Directory of Open Access Journals (Sweden)

    Anna C. Bolders

    2012-04-01

    Full Text Available Evaluative Conditioning (EC has hardly been tested in the auditory domain, but it is a potentially valuable research tool. In Experiment 1 we investigated whether the affective evaluation of short environmental sounds can be changed using affective words as unconditioned stimuli (US. Congruence effects on an affective priming task (APT for conditioned sounds demonstrated successful EC. Subjective ratings for sounds paired with negative words changed accordingly. In Experiment 2 we investigated whether the acquired valence remains stable after repeated presentation of the conditioned sound without the US or whether extinction occurs. The acquired affective value remained present, albeit weaker, even after 40 extinction trials. These results warrant the use of EC to study processing of short environmental sounds with acquired valence, even if this requires repeated stimulus presentations. This paves the way for studying processing of affective environmental sounds while effectively controlling low level-stimulus properties.

  11. Pion valence-quark parton distribution function

    Directory of Open Access Journals (Sweden)

    Lei Chang

    2015-10-01

    Full Text Available Within the Dyson–Schwinger equation formulation of QCD, a rainbow ladder truncation is used to calculate the pion valence-quark distribution function (PDF. The gap equation is renormalized at a typical hadronic scale, of order 0.5 GeV, which is also set as the default initial scale for the pion PDF. We implement a corrected leading-order expression for the PDF which ensures that the valence-quarks carry all of the pion's light-front momentum at the initial scale. The scaling behavior of the pion PDF at a typical partonic scale of order 5.2 GeV is found to be (1−xν, with ν≃1.6, as x approaches one.

  12. Masked emotional priming beyond global valence activations.

    Science.gov (United States)

    Rohr, Michaela; Degner, Juliane; Wentura, Dirk

    2012-01-01

    An immense body of research demonstrates that emotional facial expressions can be processed unconsciously. However, it has been assumed that such processing takes place solely on a global valence-based level, allowing individuals to disentangle positive from negative emotions but not the specific emotion. In three studies, we investigated the specificity of emotion processing under conditions of limited awareness using a modified variant of an affective priming task. Faces with happy, angry, sad, fearful, and neutral expressions were presented as masked primes for 33 ms (Study 1) or 14 ms (Studies 2 and 3) followed by emotional target faces (Studies 1 and 2) or emotional adjectives (Study 3). Participants' task was to categorise the target emotion. In all three studies, discrimination of targets was significantly affected by the emotional primes beyond a simple positive versus negative distinction. Results indicate that specific aspects of emotions might be automatically disentangled in addition to valence, even under conditions of subjective unawareness.

  13. Investigation of polarization effects in the gramicidin A channel from ab initio molecular dynamics simulations.

    Science.gov (United States)

    Timko, Jeff; Kuyucak, Serdar

    2012-11-28

    Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K(+) ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K(+) ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K(+) ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K(+) ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.

  14. Pauling bond strength, bond length and electron density distribution

    Energy Technology Data Exchange (ETDEWEB)

    Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, M. A.

    2014-01-18

    A power law regression equation, = 1.46(<ρ(rc)>/r)-0.19, connecting the average experimental bond lengths, , with the average accumulation of the electron density at the bond critical point, <ρ(rc)>, between bonded metal M and oxygen atoms, determined at ambient conditions for oxide crystals, where r is the row number of the M atom, is similar to the regression equation R(M-O) = 1.39(ρ(rc)/r)-0.21 determined for three perovskite crystals for pressures as high as 80 GPa. The two equations are also comparable with those, = 1.43(/r)-0.21, determined for a large number of oxide crystals at ambient conditions and = 1.39(/r)-0.22, determined for geometry optimized hydroxyacid molecules, that connect the bond lengths to the average Pauling electrostatic bond strength, , for the M-O bonded interactions. On the basis of the correspondence between the two sets of equations connecting ρ(rc) and the Pauling bond strength s with bond length, it appears that Pauling’s simple definition of bond strength closely mimics the accumulation of the electron density between bonded pairs of atoms. The similarity of the expressions for the crystals and molecules is compelling evidence that the M-O bonded interactions for the crystals and molecules 2 containing the same bonded interactions are comparable. Similar expressions, connecting bond lengths and bond strength, have also been found to hold for fluoride, nitride and sulfide molecules and crystals. The Brown-Shannon bond valence, σ, power law expression σ = [R1/(R(M-O)]N that has found wide use in crystal chemistry, is shown to be connected to a more universal expression determined for oxides and the perovskites, <ρ(rc)> = r[(1.41)/]4.76, demonstrating that the bond valence for a bonded interaction is likewise closely connected to the accumulation of the electron density between the bonded atoms. Unlike the Brown-Shannon expression, it is universal in that it holds for the M

  15. 5th International Conference on Valence Fluctuations

    CERN Document Server

    Malik, S

    1987-01-01

    During the Koln meeting (August 28-31, 1984), Irdia was chosen as the venue for the next International Conference on Valence Fluctuations. lhis was in recognition ard appreciation of the work done, both experimental ard theoretical, by the Irdian scientists in this area during the last decade. We decided to hold this Conference in the month of January, 1987 at Bangalore. lhe subject of Valence Fluctuations has kept itself alive ard active as it has provided many shocks ard suprises particularly among the Ce- ard U-based intermetallies. lhe richness of many interesting physical phenomena occurring in mixed valent materials, the flexibility of modifying their physical properties (by alloying, for example) ard the possibility of synthesizing a wide variety of new such materials seem to be the key factors in this regard. Barely six months before this Conference, an International Conference on Anomalous Rare Earths and Actinides (ICAREA) had been held at Grenoble (July, 1986) which also focussed on mixed valence a...

  16. Stark spectroscopy of mixed-valence systems.

    Science.gov (United States)

    Silverman, Lisa N; Kanchanawong, Pakorn; Treynor, Thomas P; Boxer, Steven G

    2008-01-13

    Many mixed-valence systems involve two or more states with different electric dipole moments whose magnitudes depend upon the charge transfer distance and the degree of delocalization; these systems can be interconverted by excitation of an intervalence charge transfer transition. Stark spectroscopy involves the interaction between the change in dipole moment of a transition and an electric field, so the Stark spectra of mixed-valence systems are expected to provide quantitative information on the degree of delocalization. In limiting cases, a classical Stark analysis can be used, but in intermediate cases the analysis is much more complex because the field affects not only the band position but also the intrinsic bandshape. Such non-classical Stark effects lead to widely different bandshapes. Several examples of both classes are discussed. Because electric fields are applied to immobilized samples, complications arise from inhomogeneous broadening, along with other effects that limit our ability to extract unique parameters in some cases. In the case of the radical cation of the special pair in photosynthetic reaction centres, where the mixed-valence system is in a very complex but structurally well-defined environment, a detailed analysis can be performed.

  17. Bond Issues.

    Science.gov (United States)

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

  18. Electron Transport through Polyene Junctions in between Carbon Nanotubes: an Ab Initio Realization

    Science.gov (United States)

    Chen, Yiing-Rei; Chen, Kai-Yu; Dou, Kun-Peng; Tai, Jung-Shen; Lee, Hsin-Han; Kaun, Chao-Cheng

    With both ab initio and tight-binding model calculations, we study a system of polyene bridged armchair carbon nanotube electrodes, considering one-polyene and two-polyene cases, to address aspects of quantum transport through junctions with multiple conjugated molecules. The ab initio results of the two-polyene cases not only show the interference effect in transmission, but also the sensitive dependence of such effect on the combination of relative contact sites, which agrees nicely with the tight-binding model. Moreover, we show that the discrepancy mainly brought by ab initio relaxation provides an insight into the influence upon transmission spectra, from the junction's geometry, bonding and effective potential. This work was supported by the Ministry of Science and Technology of the Republic of China under Grant Nos. 99-2112-M-003-012-MY2 and 103-2622-E-002-031, and the National Center for Theoretical Sciences of Taiwan.

  19. Time-resolved four-wave-mixing spectroscopy for inner-valence transitions.

    Science.gov (United States)

    Ding, Thomas; Ott, Christian; Kaldun, Andreas; Blättermann, Alexander; Meyer, Kristina; Stooss, Veit; Rebholz, Marc; Birk, Paul; Hartmann, Maximilian; Brown, Andrew; Van Der Hart, Hugo; Pfeifer, Thomas

    2016-02-15

    Noncollinear four-wave-mixing (FWM) techniques at near-infrared (NIR), visible, and ultraviolet frequencies have been widely used to map vibrational and electronic couplings, typically in complex molecules. However, correlations between spatially localized inner-valence transitions among different sites of a molecule in the extreme ultraviolet (XUV) spectral range have not been observed yet. As an experimental step toward this goal, we perform time-resolved FWM spectroscopy with femtosecond NIR and attosecond XUV pulses. The first two pulses (XUV-NIR) coincide in time and act as coherent excitation fields, while the third pulse (NIR) acts as a probe. As a first application, we show how coupling dynamics between odd- and even-parity, inner-valence excited states of neon can be revealed using a two-dimensional spectral representation. Experimentally obtained results are found to be in good agreement with ab initio time-dependent R-matrix calculations providing the full description of multielectron interactions, as well as few-level model simulations. Future applications of this method also include site-specific probing of electronic processes in molecules.

  20. Time-resolved four-wave-mixing spectroscopy for inner-valence transitions

    CERN Document Server

    Ding, Thomas; Kaldun, Andreas; Blättermann, Alexander; Meyer, Kristina; Stooß, Veit; Rebholz, Marc; Birk, Paul; Hartmann, Maximilian; Brown, Andrew; Van Der Hart, Hugo; Pfeifer, Thomas

    2015-01-01

    Non-collinear four-wave mixing (FWM) techniques at near-infrared (NIR), visible, and ultraviolet frequencies have been widely used to map vibrational and electronic couplings, typically in complex molecules. However, correlations between spatially localized inner-valence transitions among different sites of a molecule in the extreme ultraviolet (XUV) spectral range have not been observed yet. As an experimental step towards this goal we perform time-resolved FWM spectroscopy with femtosecond NIR and attosecond XUV pulses. The first two pulses (XUV-NIR) coincide in time and act as coherent excitation fields, while the third pulse (NIR) acts as a probe. As a first application we show how coupling dynamics between odd- and even-parity inner-valence excited states of neon can be revealed using a two-dimensional spectral representation. Experimentally obtained results are found to be in good agreement with ab initio time-dependent R-matrix calculations providing the full description of multi-electron interactions,...

  1. Competition of hydrogen bonds and halogen bonds in complexes of hypohalous acids with nitrogenated bases.

    Science.gov (United States)

    Alkorta, Ibon; Blanco, Fernando; Solimannejad, Mohammad; Elguero, Jose

    2008-10-30

    A theoretical study of the complexes formed by hypohalous acids (HOX, X = F, Cl, Br, I, and At) with three nitrogenated bases (NH 3, N 2, and NCH) has been carried out by means of ab initio methods, up to MP2/aug-cc-pVTZ computational method. In general, two minima complexes are found, one with an OH...N hydrogen bond and the other one with a X...N halogen bond. While the first one is more stable for the smallest halogen derivatives, the two complexes present similar stabilities for the iodine case and the halogen-bonded structure is the most stable one for the hypoastatous acid complexes.

  2. Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study.

    Science.gov (United States)

    Kobyłecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

    2008-01-28

    The propensity of four representative conformations of 2(')-deoxyadenosine-5(')-monophosphate (5(')-dAMPH) to bind an excess electron has been studied at the B3LYP6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5(')-dAMPH form adiabatically stable anions. The type of an anionic 5(')-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4(')-C5(') bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5(')-dAMPH(-) measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

  3. Thermal Recombination: Beyond the Valence Quark Approximation

    CERN Document Server

    Müller, B; Bass, S A

    2005-01-01

    Quark counting rules derived from recombination models agree well with data on hadron production at intermediate transverse momenta in relativistic heavy-ion collisions. They convey a simple picture of hadrons consisting only of valence quarks. We discuss the inclusion of higher Fock states that add sea quarks and gluons to the hadron structure. We show that, when recombination occurs from a thermal medium, hadron spectra remain unaffected by the inclusion of higher Fock states. However, the quark number scaling for elliptic flow is somewhat affected. We discuss the implications for our understanding of data from the Relativistic Heavy Ion Collider.

  4. NATO Advanced Study Institute on Mixed-Valence Compounds : Theory and Applications in Chemistry, Physics, Geology, and Biology

    CERN Document Server

    1980-01-01

    It has been a decade since two seminal reviews demonstrated that mixed-valence compounds share many unique and fascinating features. The insight pro­ vided by those early works has promoted a great deal of both experimental and theoretical study. As a result of extensive efforts, our understanding of the bonding and properties of mixed-valence compounds has advanced substantially. There has been no compre­ hensive treatment of mixed-valence compounds since 1967, and the meeting convened at Oxford in September, 1979, provided a unique opportunity to examine the subject and its many ramifications. Mixed-valence compounds play an important role in many fields. Although the major impact of the subject has been in chemistry, its importance has become increasingly clear in solid state physics, geology, and biology. Extensive interest and effort in the field of molecular metals has demonstrated that mixed-valency is a prerequisite for high elec­ trical conductivity. The intense colors of many minerals have been s...

  5. Parental Bonding

    Directory of Open Access Journals (Sweden)

    T. Paul de Cock

    2014-08-01

    Full Text Available Estimating the early parent–child bonding relationship can be valuable in research and practice. Retrospective dimensional measures of parental bonding provide a means for assessing the experience of the early parent–child relationship. However, combinations of dimensional scores may provide information that is not readily captured with a dimensional approach. This study was designed to assess the presence of homogeneous groups in the population with similar profiles on parental bonding dimensions. Using a short version of the Parental Bonding Instrument (PBI, three parental bonding dimensions (care, authoritarianism, and overprotection were used to assess the presence of unobserved groups in the population using latent profile analysis. The class solutions were regressed on 23 covariates (demographics, parental psychopathology, loss events, and childhood contextual factors to assess the validity of the class solution. The results indicated four distinct profiles of parental bonding for fathers as well as mothers. Parental bonding profiles were significantly associated with a broad range of covariates. This person-centered approach to parental bonding has broad utility in future research which takes into account the effect of parent–child bonding, especially with regard to “affectionless control” style parenting.

  6. The Hydration Structure of Carbon Monoxide by Ab Initio Methods

    CERN Document Server

    Awoonor-Williams, Ernest

    2016-01-01

    The solvation of carbon monoxide (CO) in liquid water is important for understanding its toxicological effects and biochemical roles. In this paper, we use ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations to assess the accuracy of the Straub and Karplus molecular mechanical (MM) model for CO(aq). The CCSD(T)-F12 CO--H2O potential energy surfaces show that the most stable structure corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface it incorrectly predicts that the O atom is a stronger hydrogen bond acceptor than the C atom. The AIMD simulations indicate that CO is solvated like a hydrophobic solute, with very limited hydrogen bonding with water. The MM model tends to overestimate the degree of hydrogen bonding and overestimates the atomic radius of the C atom. The calculated Gibbs energy of hydration is in good agreement with experiment (9.3 kJ/mol calc. vs 10.7 kJ/mol exptl.). The calculated diffusivity of CO(aq) in TIP3P-model water was 5.19 x 10-5 cm2/s ...

  7. Stress reduction of Cu-doped diamond-like carbon films from ab initio calculations

    Directory of Open Access Journals (Sweden)

    Xiaowei Li

    2015-01-01

    Full Text Available Structure and properties of Cu-doped diamond-like carbon films (DLC were investigated using ab initio calculations. The effect of Cu concentrations (1.56∼7.81 at.% on atomic bond structure was mainly analyzed to clarify the residual stress reduction mechanism. Results showed that with introducing Cu into DLC films, the residual compressive stress decreased firstly and then increased for each case with the obvious deterioration of mechanical properties, which was in agreement with the experimental results. Structural analysis revealed that the weak Cu-C bond and the relaxation of both the distorted bond angles and bond lengths accounted for the significant reduction of residual compressive stress, while at the higher Cu concentration the increase of residual stress attributed to the existence of distorted Cu-C structures and the increased fraction of distorted C-C bond lengths.

  8. Stress reduction of Cu-doped diamond-like carbon films from ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiaowei; Ke, Peiling; Wang, Aiying, E-mail: aywang@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2015-01-15

    Structure and properties of Cu-doped diamond-like carbon films (DLC) were investigated using ab initio calculations. The effect of Cu concentrations (1.56∼7.81 at.%) on atomic bond structure was mainly analyzed to clarify the residual stress reduction mechanism. Results showed that with introducing Cu into DLC films, the residual compressive stress decreased firstly and then increased for each case with the obvious deterioration of mechanical properties, which was in agreement with the experimental results. Structural analysis revealed that the weak Cu-C bond and the relaxation of both the distorted bond angles and bond lengths accounted for the significant reduction of residual compressive stress, while at the higher Cu concentration the increase of residual stress attributed to the existence of distorted Cu-C structures and the increased fraction of distorted C-C bond lengths.

  9. Reducing the negative valence of stressful memories through emotionally valenced, modality-specific tasks

    NARCIS (Netherlands)

    Tadmor, Avia; McNally, Richard J; Engelhard, Iris M

    2016-01-01

    BACKGROUND AND OBJECTIVES: People who perform a cognitively demanding secondary task while recalling a distressing memory often experience the memory as less emotional, vivid, or accurate during subsequent recollections. In this experiment, we tested whether the emotional valence (positive versus ne

  10. Study of nonplanarity of peptide bond using theoretical calculations.

    Science.gov (United States)

    Selvarengan, P; Kolandaivel, P

    2005-08-01

    The conformational dependence of nonplanarity of the peptide bond of formylglycinamide has been studied using ab initio and density functional theory methods. Hartree-Fock self-consistent field theory (HF), Møller-Plesset perturbation theory (MP2) of ab initio and B3LYP level of theory of dft method have been used employing 6-31++G** basis set. The MP2 method predicts better results than HF and B3LYP levels of theory for conformational stability dependence of nonplanarity. Systematic dependence of planarity deviation has been observed in MP2 theory. The chemical hardness values successfully predict the conformational region, but fail to obey maximum hardness principle. It is concluded that the most reliable dft method could not successfully predict the planarity of peptide bond in comparison with electron correlated method of ab initio method.

  11. Electronic Structure and Physical-Chemistry Property Relationship for Oxazole Derivatives by Ab Initio and DFT Methods

    OpenAIRE

    2011-01-01

    The geometric, electronic structure, effect of the substitution, and structure physical-chemistry relationship for oxazoles derivatives have been studied by ab initio and DFT theory. In the present work, the calculated values, namely, net charges, bond lengths, dipole moments, electron affinities, heats of formation, and QSAR properties are reported and discussed in terms of the reactivity of oxazole derivatives.

  12. Electronic Structure and Physical-Chemistry Property Relationship for Oxazole Derivatives by Ab Initio and DFT Methods

    Directory of Open Access Journals (Sweden)

    Salah Belaidi

    2011-01-01

    Full Text Available The geometric, electronic structure, effect of the substitution, and structure physical-chemistry relationship for oxazoles derivatives have been studied by ab initio and DFT theory. In the present work, the calculated values, namely, net charges, bond lengths, dipole moments, electron affinities, heats of formation, and QSAR properties are reported and discussed in terms of the reactivity of oxazole derivatives.

  13. The valence electron structure and property analysis of TiC

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The valence electron structure of TiC was calculated by using the empirical electron theory of solids and molecules. The calculated results show that with the increase of temperature the number of common electrons of TiC increases, which indicates that TiC has a good thermal sta-bility; and there exists a close relationship between hardness and brittleness of TiC. According to the number of lattice electrons, the differences among the crystals with different structures can be explained qualitatively. Using the "bond- strengthening factor", the differences of hardness among the crystals with different structures can also be qualitatively explained to some extent.

  14. Ab initio molecular dynamics simulation of hydrogen fluoride at several thermodynamic states

    DEFF Research Database (Denmark)

    Kreitmeir, M.; Bertagnolli, H.; Mortensen, Jens Jørgen;

    2003-01-01

    Liquid hydrogen fluoride is a simple but interesting system for studies of the influence of hydrogen bonds on physical properties. We have performed ab initio molecular dynamics simulations of HF at several thermodynamic states, where we examine the microscopic structure of the liquid as well...... as its static and dynamic properties. The results obtained show good agreement with well established data, and, moreover, we were able to show significant changes within the structure depending on the system's temperature and density....

  15. Raman and ab initio studies of simple and binary 1-alkyl-3-methylimidazolium ionic liquids

    DEFF Research Database (Denmark)

    Berg, R.W.; Deetlefs, M.; Seddon, K.R.

    2005-01-01

    Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C(6)mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2...... bonding between the imidazolium headgroup and the anions, and the invariance of the essentially 50:50 mixture of the predominant conformers informs on the nature of glass formation in these systems....

  16. Self-doping of molecular quantum-dot cellular automata: mixed valence zwitterions.

    Science.gov (United States)

    Lu, Yuhui; Lent, Craig

    2011-09-07

    Molecular quantum-dot cellular automata (QCA) is a promising paradigm for realizing molecular electronics. In molecular QCA, binary information is encoded in the distribution of intramolecular charge, and Coulomb interactions between neighboring molecules combine to create long-range correlations in charge distribution that can be exploited for signal transfer and computation. Appropriate mixed-valence species are promising candidates for single-molecule device operation. A complication arises because many mixed-valence compounds are ions and the associated counterions can potentially disrupt the correct flow of information through the circuit. We suggest a self-doping mechanism which incorporates the counterion covalently into the structure of a neutral molecular cell, thus producing a zwitterionic mixed-valence complex. The counterion is located at the geometrical center of the QCA molecule and bound to the working dots via covalent bonds, thus avoiding counterion effects that bias the system toward one binary information state or the other. We investigate the feasibility of using multiply charged anion (MCA) boron clusters, specifically closo-borate dianion, as building blocks. A first principle calculation shows that neutral, bistable, and switchable QCA molecules are possible. The self-doping mechanism is confirmed by molecular orbital analysis, which shows that MCA counterions can be stabilized by the electrostatic interaction between negatively charged counterions and positively charged working dots. This journal is © the Owner Societies 2011

  17. Mulliken-Hush analysis of a bis(triarylamine) mixed-valence system with a N...N distance of 28.7 A.

    Science.gov (United States)

    Heckmann, Alexander; Amthor, Stephan; Lambert, Christoph

    2006-07-28

    An organic mixed valence compound with a spacer length of 25 unsaturated bonds separating two amine redox centres was synthesised and the electron transfer behaviour was investigated in the context of a Mulliken-Hush analysis in order to estimate the longest redox centre separation for which an intervalence charge transfer band can be observed.

  18. Electronic Band Structure of Transition Metal Dichalcogenides from Ab Initio and Slater–Koster Tight-Binding Model

    Directory of Open Access Journals (Sweden)

    Jose Ángel Silva-Guillén

    2016-10-01

    Full Text Available Semiconducting transition metal dichalcogenides present a complex electronic band structure with a rich orbital contribution to their valence and conduction bands. The possibility to consider the electronic states from a tight-binding model is highly useful for the calculation of many physical properties, for which first principle calculations are more demanding in computational terms when having a large number of atoms. Here, we present a set of Slater–Koster parameters for a tight-binding model that accurately reproduce the structure and the orbital character of the valence and conduction bands of single layer MX 2 , where M = Mo, W and X = S, Se. The fit of the analytical tight-binding Hamiltonian is done based on band structure from ab initio calculations. The model is used to calculate the optical conductivity of the different compounds from the Kubo formula.

  19. Atomic volume, atomic distances and chemical bonding in solid metallic elements; Atomvolumen, Atomabstaende und chemische Bindung in festen metallischen Elementen

    Energy Technology Data Exchange (ETDEWEB)

    Troemel, M.; Huebner, S. [Frankfurt Univ. (Germany). Inst. fuer Anorganische Chemie

    2001-05-01

    Relationships between bond lengths and bond numbers and also between atomic volumes and valencies are derived and parameters for their calculation are given for the s-block, p-block, and d-block metals. From the atomic volumes under pressure, the valencies of three solid lanthanoids have been confirmed or redetermined: La 3; Ce 2, 3, and 4; Yb 2 and 3. (orig.)

  20. Valency, Secondary Frequency, and Lexical Access: A Japanese Study.

    Science.gov (United States)

    Yamada, Jun; Kayamoto, Yuriko

    1998-01-01

    A study examined the effects of valency (associative value representing the number of two-kanji words containing the first-positional kanji of the word) on recognition of two-kanji words in Japanese. Frequency and valency of the first constituent kanji were significant factors for word recognition, and frequency of the first constituent kanji was…

  1. Prediction of valence and arousal from music features

    NARCIS (Netherlands)

    Den Brinker, A.C.; Van Dinther, C.H.B.A.; Skowronek, J.

    2011-01-01

    Mood is an important attribute of music and knowledge on mood can beused as a basic ingredient in music recommender and retrieval systems. Moods are assumed to be dominantly determined by two dimensions:valence and arousal. An experiment was conducted to attain data forsong-based ratings of valence

  2. Static and Dynamical Valence-Charge-Density Properties of GaAs

    Science.gov (United States)

    Pietsch, Ullrich

    1993-02-01

    Owing to the close neighbourhood of Ga and As in Mendeleev's table, GaAs shows two fundamental classes of X-ray structure amplitudes distinguished by their extremely different scattering power. They are differently sensitive to the valence electron density (VED) redistribution caused by the chemical bond and must be measured by different experimental methods. Using such data, both the VED and the difference electron densities (DED) are calculated here. Comparison with theoret-ical densities shows that the VED is characterized by covalent, ionic and metallic contributions. The DED constructed from GaAs and Ge data demonstrates the electronic response caused by a "protonic" charge transfer between both f.c.c. sublattices as well as the transition from a purely covalent to a mixed covalent-ionic bond. Especially the charge-density accumulation between nearest neighbours (bond charge (BC)) depends on the distance between the bonding atoms and changes under the influence of any lattice deformation. This phenomenon is described by a BC-transfer model. Its direct experimental proof is given by measuring the variation of the scattering power of weak reflections under the influence of an external electric field. This experiment demonstrates that the ionicity of the bond changes in addition to the BC variation.

  3. Valence and magnetic ordering in intermediate valence compounds: TmSe versus SmB(6).

    Science.gov (United States)

    Derr, J; Knebel, G; Lapertot, G; Salce, B; Méasson, M-A; Flouquet, J

    2006-02-15

    The intermediate valence systems TmSe and SmB(6) have been investigated up to 16 and 18 GPa by ac microcalorimetry with a pressure (p) tuning realized in situ at low temperature. For TmSe, the transition from an antiferromagnetic insulator for p3 GPa), T(N) is found to increase linearly with p. A similar linear p increase of T(N) is observed for the quasitrivalent compound TmS, which is at ambient pressure equivalent to TmSe at p∼7 GPa. In the case of SmB(6) long range magnetism has been detected above p∼8 GPa, i.e. at a pressure slightly higher than the pressure of the insulator to metal transition. However a homogeneous magnetic phase occurs only above 10 GPa. The magnetic and electronic properties are related to the renormalization of the 4f wavefunction either to the divalent or the trivalent configurations. As observed in SmS, long range magnetism in SmB(6) occurs already far below the pressure where a trivalent Sm(3+) state will be reached. It seems possible to describe roughly the physical properties of the intermediate valence equilibrium by assuming formulae for the Kondo lattice temperature depending on the valence configuration. Comparison is also made with the appearance of long range magnetism in cerium and ytterbium heavy fermion compounds.

  4. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen,and Zhejiang and Guangdong provinces to issue bonds for the first time.How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the Shanghai Securities Journal.Edited excerpts follow.

  5. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen, and Zhejiang and Guangdong provinces to issue bonds for the first time. How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the ShanghaiSecuritiesJournal. Edited excerpts follow:

  6. The Crystal Structure of Impurity Centers Tm^{2+} and Eu^{2+} in SrCl2: Ab Initio Calculations

    Science.gov (United States)

    Chernyshev, V. A.; Serdcev, A. V.; Petrov, V. P.; Nikiforov, A. E.

    2016-12-01

    Ab initio calculations of the impurity centers Tm^{2+} thulium and europium Eu^{2+} in SrCl2 and MeF2 (Me = Ca, Sr, Ba) were carried out at low (zero) temperature. The crystal structure of impurity centers was investigated. Charge density maps show that the bonds formed by the rare-earth ions have an ionic character. The crystal structures, lattice dynamics, and band structures of MeF2 and SrCl2 were calculated at low temperature. Ab initio calculations were performed in periodic CRYSTAL code within the framework of the MO LCAO approach by using hybrid DFT functionals.

  7. Effect of phenyl and benzyl group in heterocyclic dithiocarbamates on the ZnS 4N chromophore: Synthesis, spectral, valence-bond parameters and single crystal X-ray structural studies on (pyridine)bis(1,2,3,4-tetrahydroquinolinedithiocarbamato)zinc(II) and (pyridine)bis(1,2,3,4-tetrahydroisoquinolinedithiocarbamato)zinc(II)

    Science.gov (United States)

    Srinivasan, N.; Thirumaran, S.; Ciattini, Samuele

    2009-03-01

    Two Zn(II)dithiocarbamates with ZnS 4N chromophores have been synthesized ([Zn(thqdtc) 2(py)] ( 1) and [Zn(thiqdtc) 2(py)] ( 2) (where thqdtc = 1,2,3,4-tetrahydroquinolinedithiocarbamate, thiqtc = 1,2,3,4-tetrahydroisoquinolinedithiocarbamate and py = pyridine)) from [Zn(thqdtc) 2] ( 3) and [Zn(thiqdtc) 2] ( 4), respectively. Their structures and properties have been characterized by IR and NMR spectra. The structures of both the complexes were determined by single crystal X-ray crystallography. The observed deshielding of the H-2 protons for 1 and 3 and H-1 and H-3 protons for 2 and 4 in the 1H NMR spectra is attributed to the drift of electrons from the nitrogen of the NR 2 group, forcing a high electron density towards sulfur via the thioureide π-system. In the 13C NMR spectra, the most important thioureide (N 13CS 2) carbon signals are observed in the region 204-207 ppm. The upfield shift of NCS 2 carbon signal for 1 (204.2 ppm) from the chemical shift value of 2 (206.9 ppm) is due to electron withdrawing resonance effect of phenyl ring thereby decreasing the double bond character in tetrahydroquinolinedithiocarbamate, whereas benzyl group in tetrahydroisoquinolinedithiocarbamate cannot participate in resonance delocalization in the same way. Single crystal X-ray structural analysis of 1 and 2 showed that the zinc atom is pentacoordinated with four sulfur atoms from the dithiocarbamate ligands and one nitrogen atom from the pyridine. VBS values support the correctness of the determined structure. The lower VBS value of 2 is due to the steric effect exerted by the thiqdtc. The phenyl and benzyl group in the heterocyclic dithiocarbamates influences the electronic properties of 1 and 2. The shift of ν C- N(thioureide) and thioureide N 13CS 2 carbon signals are correlated with the electronic effects of the dithiocarbamate ligands.

  8. VALENCY AND SYNTACTICAL RELATION IN BIMANESS

    Directory of Open Access Journals (Sweden)

    Made Sri Satyawati

    2012-11-01

    Full Text Available This study presents the findings and descriptions of the replies to severalproblems that have not been completely and deeply discussed in the researchespreviously conducted on Bimanese. The problems are related to micro-linguistic factors,namely valency and syntactical relation in Bimanese. Both deductive and inductiveapproaches were applied to obtain satisfactory results. The main theory employed in thisstudy is Role and Reference Grammar Theory (RRG by Van Valin and J. Lapolla. It wasemployed to completely analyze the collected data in accordance with the problemsproposed in this research, and the inductive approach was employed to analyze the datain order to get novelties.In this study, clause structure is given the first priority to discuss, followed by thediscussion on operator, voice markers, nominalizers, and definiteness. Based on thepredicate category, the clause in Bimanese can be constructed with the constituents thatare under the categories of verb, noun, adjective, number, and adverb (prepositionalphrase. Based on the clause analysis, it has been found that in Bimanese there are severaloperators, each of which has different functional boundary in marking the clausemeaning. One operator may only sign nucleus, core (nucleus and argument, or core andperiphery. Bimanese has also been identified to have four linguistic states expressed byverbs that are made to make sense based on state (Aktisontrat, achievement, andaccomplishment. RRG classifies verbs into ten instead of four. However, in this study, tomake the analysis easier, verbs are classified into four. The predicate in Bimanese can beboth serial verbs and secondary verbs. It has also been found that the mechanism ofchange in valency is marked by the attachment of markers to the verbs resulting incausativity, applicativity, and resultivity. From those syntactical constructions, thesyntactical relation in Bimanese can be clearly identified. The discussion on syntacticalrelation

  9. Chemical Bond Parameters in Sr3MRhO6 (M=Rare earth)

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Chemical bond parameters, that is, bond covalency, bond valence, macroscopic linear susceptibility, and oxidation states of elements in Sr3MRhO6 (M=Sm, Eu, Tb, Dy, Ho, Er, Yb) have been calculated. The results indicate that the bond covalency of M-O decreases sharply with the decrease of ionic radius of M3+ from Sm to Yb, while no obvious trend has been found for Rh-O and Sr-O bonds. The global instability index indicates that the crystal structures of Sr3MrhO6 (M = Sm, Eu, Tb, Dy, Ho) have strained bonds.

  10. Valence electron structure and properties of the ZrO2

    Institute of Scientific and Technical Information of China (English)

    LI JinPing; MENG SongHe; HAN JieCai; ZHANG XingHong

    2008-01-01

    To reveal the properties of ZrO2 at the atom and electron levels, the valence elec-tron structures of three ZrO2 phases were analyzed on the basis of the empirical electron theory of solids and molecules. The results showed that the hybridization levels of Zr and O atoms in the m-ZrO2 were the same as those in the t-ZrO2, while those in the c-ZrO2 rose markedly. The electron numbers and bond energies on the strongest covalent bonds in the m-ZrO2 phase were the greatest, the values were 0.901106 and 157.5933 kJ/mol, respectively. Those in the t-ZrO2 phase took second place, which were 0.722182 and 123.9304 kJ/mol, and those in the c-ZrO2 phase were the smallest, which were 0.469323 and 79.0289 kJ/mol. According to the product of the bond energy on the strongest covalent bond and equivalent bond number (this value reflected the crystal cohesive energy), the order from the greatness to smallness was the c-ZrO2 t-ZrO2 m-ZrO2. This showed that the m-phase bonds were the tightest, their energy was the smallest, the crystal cohe-sive energy of the m-phase was the largest, and the m-phase existed most stably at room temperature. So it must need energy or higher temperature to take apart the stronger covalent bonds to form a new phase.

  11. One Way to Design a Valence-Skip Compound

    Science.gov (United States)

    Hase, I.; Yanagisawa, T.; Kawashima, K.

    2017-02-01

    Valence-skip compound is a good candidate with high T c and low anisotropy because it has a large attractive interaction at the site of valence-skip atom. However, it is not easy to synthesize such compound because of (i) the instability of the skipping valence state, (ii) the competing charge order, and (iii) that formal valence may not be true in some compounds. In the present study, we show several examples of the valence-skip compounds and discuss how we can design them by first principles calculations. Furthermore, we calculated the electronic structure of a promising candidate of valence skipping compound RbTlCl3 from first principles. We confirmed that the charge-density wave (CDW) is formed in this compound, and the Tl atoms in two crystallographic different sites take the valence Tl1+ and Tl3+. Structure optimization study reveals that this CDW is stable at the ambient pressure, while this CDW gap can be collapsed when we apply pressure with several gigapascals. In this metallic phase, we can expect a large charge fluctuation and a large electron-phonon interaction.

  12. Positron annihilation with core and valence electrons

    CERN Document Server

    Green, D G

    2015-01-01

    $\\gamma$-ray spectra for positron annihilation with the core and valence electrons of the noble gas atoms Ar, Kr and Xe is calculated within the framework of diagrammatic many-body theory. The effect of positron-atom and short-range positron-electron correlations on the annihilation process is examined in detail. Short-range correlations, which are described through non-local corrections to the vertex of the annihilation amplitude, are found to significantly enhance the spectra for annihilation on the core orbitals. For Ar, Kr and Xe, the core contributions to the annihilation rate are found to be 0.55\\%, 1.5\\% and 2.2\\% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. Importantly however, the core subshells have a broad momentum distribution and markedly contribute to the annihilation spectra at Doppler energy shifts $\\gtrsim3$\\,keV, and even dominate the spectra of Kr and Xe at shifts $\\gtrsim5$\\,keV. Their inclusion brings the theoretical ...

  13. Valence Parity Renders z•-Type Ions Chemically Distinct

    OpenAIRE

    Hubler, Shane L.; Jue, April; Keith, Jason; McAlister, Graeme C.; Craciun, Gheorghe; Coon, Joshua J.

    2008-01-01

    Here we report that the odd electron z•-type ions formed by the electron-based peptide dissociation methods (electron capture or transfer, ECD or ETD) have distinctive chemical compositions from other common product ion types. Specifically, b-, c-, and y-type ions have an odd number of atoms with an odd valence (e.g., N and H), while z•-type ions contain an even number of atoms with an odd valence. This tenet, referred to as the valence parity rule, mandates that no c-type ion shall have the ...

  14. Fast and accurate predictions of covalent bonds in chemical space

    Science.gov (United States)

    Chang, K. Y. Samuel; Fias, Stijn; Ramakrishnan, Raghunathan; von Lilienfeld, O. Anatole

    2016-05-01

    We assess the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among molecules. We have investigated σ bonding to hydrogen, as well as σ and π bonding between main-group elements, occurring in small sets of iso-valence-electronic molecules with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order Taylor expansions of covalent bonding potentials can achieve high accuracy if (i) the alchemical interpolation is vertical (fixed geometry), (ii) it involves elements from the third and fourth rows of the periodic table, and (iii) an optimal reference geometry is used. This leads to near linear changes in the bonding potential, resulting in analytical predictions with chemical accuracy (˜1 kcal/mol). Second order estimates deteriorate the prediction. If initial and final molecules differ not only in composition but also in geometry, all estimates become substantially worse, with second order being slightly more accurate than first order. The independent particle approximation based second order perturbation theory performs poorly when compared to the coupled perturbed or finite difference approach. Taylor series expansions up to fourth order of the potential energy curve of highly symmetric systems indicate a finite radius of convergence, as illustrated for the alchemical stretching of H 2+ . Results are presented for (i) covalent bonds to hydrogen in 12 molecules with 8 valence electrons (CH4, NH3, H2O, HF, SiH4, PH3, H2S, HCl, GeH4, AsH3, H2Se, HBr); (ii) main-group single bonds in 9 molecules with 14 valence electrons (CH3F, CH3Cl, CH3Br, SiH3F, SiH3Cl, SiH3Br, GeH3F, GeH3Cl, GeH3Br); (iii) main-group double bonds in 9 molecules with 12 valence electrons (CH2O, CH2S, CH2Se, SiH2O, SiH2S, SiH2Se, GeH2O, GeH2S, GeH2Se); (iv) main-group triple bonds in 9 molecules with 10 valence electrons (HCN, HCP, HCAs, HSiN, HSi

  15. Bond-length distributions for ions bonded to oxygen: alkali and alkaline-earth metals.

    Science.gov (United States)

    Gagné, Olivier Charles; Hawthorne, Frank Christopher

    2016-08-01

    [4]- and [6]-coordination, Na(+) in [4]- and [6]-coordination. For alkali-metal and alkaline-earth-metal ions, there is a positive correlation between cation coordination number and the grand mean incident bond-valence sum at the central cation, the values varying from 0.84 v.u. for ([5])K(+) to 1.06 v.u. for ([8])Li(+), and from 1.76 v.u. for ([7])Ba(2+) to 2.10 v.u. for ([12])Sr(2+). Bond-valence arguments suggest coordination numbers higher than [12] for K(+), Rb(+), Cs(+) and Ba(2+).

  16. Analysis of the valence electronic structures and calculation of the physical properties of Fe,Co,and Ni

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.

  17. Analysis of the valence electronic structures and calculation of the physical properties of Fe, Co, and Ni

    Institute of Scientific and Technical Information of China (English)

    WU WenXia; XUE ZhiYong; HONG Xing; LI XiuMei; GUO YongQuan

    2009-01-01

    The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.

  18. Coherent Control of Bond Making

    CERN Document Server

    Levin, Liat; Rybak, Leonid; Kosloff, Ronnie; Koch, Christiane P; Amitay, Zohar

    2014-01-01

    We demonstrate for the first time coherent control of bond making, a milestone on the way to coherent control of photo-induced bimolecular chemical reactions. In strong-field multiphoton femtosecond photoassociation experiments, we find the yield of detected magnesium dimer molecules to be enhanced for positively chirped pulses and suppressed for negatively chirped pulses. Our ab initio model shows that control is achieved by purification via Franck-Condon filtering combined with chirp-dependent Raman transitions. Experimental closed-loop phase optimization using a learning algorithm yields an improved pulse that utilizes vibrational coherent dynamics in addition to chirp-dependent Raman transitions. Our results show that coherent control of binary photo-reactions is feasible even under thermal conditions.

  19. Using beryllium bonds to change halogen bonds from traditional to chlorine-shared to ion-pair bonds.

    Science.gov (United States)

    Alkorta, Ibon; Elguero, José; Mó, Otilia; Yáñez, Manuel; Del Bene, Janet E

    2015-01-21

    Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the structures, binding energies, and bonding characteristics of binary complexes HFBe:FCl, R2Be:FCl, and FCl:N-base, and of ternary complexes HFBe:FCl:N-base and R2Be:FCl:N-base for R = H, F, Cl; N-base = NH3, NHCH2, NCH. Dramatic synergistic cooperative effects have been found between the Be···F beryllium bonds and the Cl···N halogen bonds in ternary complexes. The Cl···N traditional halogen bonds and the Be···F beryllium bonds in binary complexes become significantly stronger in ternary complexes, while the F-Cl bond weakens. Charge-transfer from F to the empty p(σ) orbital of Be leads to a bending of the XYBe molecule and a change in the hybridization of Be, which in the limit becomes sp(2). As a function of the intrinsic basicity of the nitrogen base and the intrinsic acidity of the Be derivative, the halogen-bond type evolves from traditional to chlorine-shared to ion-pair bonds. The mechanism by which an ion-pair complex is formed is similar to that involved in the dissociative proton attachment process. EOM-CCSD spin-spin coupling constants (1X)J(Cl-N) across the halogen bond in these complexes also provide evidence of the same evolution of the halogen-bond type.

  20. Ab initio study of heterojunction discontinuities in the ZnO/Cu2O system

    Science.gov (United States)

    Zemzemi, M.; Alaya, S.; Ben Ayadi, Z.

    2014-06-01

    Solar cells based on transparent conductive oxides such as ZnO/Cu2O constitute a very advanced way to build high-performance cells. In this work, we are interested in the characterization of the interface through nanoscale modeling based on ab initio approaches (density functional theory, local density approximation, and pseudopotential). This work aims to build a supercell containing a heterojunction ZnO/Cu2O and study the structural properties and the discontinuity of the valence band (band offset) from a semiconducting to another phase. We build a zinc oxide in the wurtzite structure along [0001] on which we place the copper oxide in the hexagonal (CdI2-type) structure. We choose the method of Van de Walle and Martin to calculate the energy offset. This approach fits well the density functional theory. Our calculation of the band offset gives a value that corresponds to other experimental and theoretical values.

  1. Precise Lifetime Measurements in Light Nuclei for Benchmarking Modern Ab-initio Nuclear Structure Models

    Energy Technology Data Exchange (ETDEWEB)

    Lister, C.J. [Department of Physics, University of Massachusetts, Lowell, Lowell MA 01854 (United States); McCutchan, E.A. [National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY 11973-5000 (United States)

    2014-06-15

    A new generation of ab-initio calculations, based on realistic two- and three-body forces, is having a profound impact on our view of how nuclei work. To improve the numerical methods, and the parameterization of 3-body forces, new precise data are needed. Electromagnetic transitions are very sensitive to the dynamics which drive mixing between configurations. We have made a series of precise (< 3%) measurements of electromagnetic transitions in the A=10 nuclei {sup 10}C and {sup 10}Be by using the Doppler Shift Attenuation method carefully. Many interesting features can be reproduced including the strong α clustering. New measurements on {sup 8}Be and {sup 12}Be highlight the interplay between the alpha clusters and their valence neutrons.

  2. Trait valence and the better-than-average effect.

    Science.gov (United States)

    Gold, Ron S; Brown, Mark G

    2011-12-01

    People tend to regard themselves as having superior personality traits compared to their average peer. To test whether this "better-than-average effect" varies with trait valence, participants (N = 154 students) rated both themselves and the average student on traits constituting either positive or negative poles of five trait dimensions. In each case, the better-than-average effect was found, but trait valence had no effect. Results were discussed in terms of Kahneman and Tversky's prospect theory.

  3. Concept of chemical bond and aromaticity based on quantum information theory

    CERN Document Server

    Szilvási, T; Legeza, Ö

    2015-01-01

    Quantum information theory (QIT) emerged in physics as standard technique to extract relevant information from quantum systems. It has already contributed to the development of novel fields like quantum computing, quantum cryptography, and quantum complexity. This arises the question what information is stored according to QIT in molecules which are inherently quantum systems as well. Rigorous analysis of the central quantities of QIT on systematic series of molecules offered the introduction of the concept of chemical bond and aromaticity directly from physical principles and notions. We identify covalent bond, donor-acceptor dative bond, multiple bond, charge-shift bond, and aromaticity indicating unified picture of fundamental chemical models from ab initio.

  4. Structural properties of liquid N-methylacetamide via ab initio, path integral, and classical molecular dynamics

    Science.gov (United States)

    Whitfield, T. W.; Crain, J.; Martyna, G. J.

    2006-03-01

    In order to better understand the physical interactions that stabilize protein secondary structure, the neat liquid state of a peptidic fragment, N-methylacetamide (NMA), was studied using computer simulation. Three different descriptions of the molecular liquid were examined: an empirical force field treatment with classical nuclei, an empirical force field treatment with quantum mechanical nuclei, and an ab initio density functional theory (DFT) treatment. The DFT electronic structure was evaluated using the BLYP approximate functional and a plane wave basis set. The different physical effects probed by the three models, such as quantum dispersion, many-body polarization, and nontrivial charge distributions on the liquid properties, were compared. Much of the structural ordering in the liquid is characterized by hydrogen bonded chains of NMA molecules. Modest structural differences are present among the three models of liquid NMA. The average molecular dipole in the liquid under the ab initio treatment, however, is enhanced by 60% over the gas phase value.

  5. Ab Initio Calculations for the BaTiO3 (001) Surface Structure

    Institute of Scientific and Technical Information of China (English)

    XUE Xu-Yan; WANG Chun-Lei; ZHONG Wei-Lie

    2004-01-01

    @@ The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field.We analyse their electronic structures (band structure, density of states and the electronic density redistribution with emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed.The band gap reduces especially for the TiO2 termination.

  6. Modelling of nuclear glasses by classical and ab initio molecular dynamics; Modelisation de verres intervenant dans le conditionnement des dechets radioactifs par dynamiques moleculaires classique et ab initio

    Energy Technology Data Exchange (ETDEWEB)

    Ganster, P

    2004-10-15

    A calcium aluminosilicate glass of molar composition 67 % SiO{sub 2} - 12 % Al{sub 2}O{sub 3} - 21 % CaO was modelled by classical and ab initio molecular dynamics. The size effect study in classical MD shows that the systems of 100 atoms are more ordered than the larger ones. These effects are mainly due to the 3-body terms in the empirical potentials. Nevertheless, these effects are small and the structures generated are in agreement with experimental data. In such kind of glass, we denote an aluminium avoidance and an excess of non bridging oxygens which can be compensated by tri coordinated oxygens. When the dynamics of systems of 100 and 200 atoms is followed by ab initio MD, some local arrangements occurs (bond length, angular distributions). Thus, more realistic vibrational properties are obtained in ab initio MD. The modelling of thin films shows that aluminium atoms extend to the most external part of the surface and they are all tri-coordinated. Calcium atoms are set in the sub layer part of the surface and they produce a depolymerization of the network. In classical MD, tri-coordinated aluminium atoms produce an important electric field above the surface. With non bridging oxygens, they constitute attractive sites for single water molecules. (author)

  7. Ab initio modelling of boron related defects in amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Tiago A.; Torres, Vitor J.B. [Department of Physics, University of Aveiro, Campus Santiago, 3810-193 Aveiro (Portugal)

    2012-10-15

    We have modeled boron related point defects in amorphous silicon, using an ab initio method, the Density functional theory-pseudopotential code Aimpro. The boron atoms were embedded in 64 atom amorphous silicon cubic supercells. The calculations were performed using boron defects in 15 different supercells. These supercells were developed using a modified Wooten-Winer-Weaire bond switching mechanism. In average, the properties of the 15 supercells agree with the observed radial and bond angle distributions, as well the electronic and vibrational density of states and Raman spectra. In amorphous silicon it has been very hard to find real self-interstitials, since for almost all the tested configurations, the amorphous lattice relaxes overall. We found that substitutional boron prefers to be 4-fold coordinated. We find also an intrinsic hole-trap in the non-doped amorphous lattice, which may explain the low efficiency of boron doping. The local vibrational modes are, in average, higher than the correspondent crystalline values (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Emotional valence and the free-energy principle.

    Directory of Open Access Journals (Sweden)

    Mateus Joffily

    Full Text Available The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

  9. Emotional valence and the free-energy principle.

    Science.gov (United States)

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

    The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

  10. On the valence fluctuation in the early actinide metals

    Energy Technology Data Exchange (ETDEWEB)

    Söderlind, P., E-mail: soderlind@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Landa, A.; Tobin, J.G.; Allen, P. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Medling, S.; Booth, C.H. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Bauer, E.D.; Cooley, J.C. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Sokaras, D.; Weng, T.-C.; Nordlund, D. [Stanford Synchrotron Radiation Lightsource, SLAC National Laboratory, Menlo Park, CA 94025 (United States)

    2016-02-15

    Highlights: • We make a connection between experimentally observed valence fluctuations and density functional theory. • We present a new model for valence fluctuations. • We present new experimental data for uranium and valence fluctuations. - Abstract: Recent X-ray measurements suggest a degree of valence fluctuation in plutonium and uranium intermetallics. We are applying a novel scheme, in conjunction with density functional theory, to predict 5f configuration fractions of states with valence fluctuations for the early actinide metals. For this purpose we perform constrained integer f-occupation calculations for the α phases of uranium, neptunium, and plutonium metals. For plutonium we also investigate the δ phase. The model predicts uranium and neptunium to be dominated by the f{sup 3} and f{sup 4} configurations, respectively, with only minor contributions from other configurations. For plutonium (both α and δ phase) the scenario is dramatically different. Here, the calculations predict a relatively even distribution between three valence configurations. The δ phase has a greater configuration fraction of f{sup 6} compared to that of the α phase. The theory is consistent with the interpretations of modern X-ray experiments and we present resonant X-ray emission spectroscopy results for α-uranium.

  11. Role of the electron transfer and magnetic exchange interactions in the magnetic properties of mixed-valence polyoxovanadate complexes.

    Science.gov (United States)

    Calzado, Carmen J; Clemente-Juan, Juan M; Coronado, Eugenio; Gaita-Arino, Alejandro; Suaud, Nicolas

    2008-07-01

    Modeling the properties of high-nuclearity, high-electron-population, mixed-valence (MV) magnetic systems remains one of the open challenges in molecular magnetism. In this work, we analyze the magnetic properties of a series of polyoxovananadate clusters of formula [V 18O 42] (12-) and [V 18O 42] (4-). The first compound is a fully localized spin cluster that contains 18 unpaired electrons located at the metal sites, while the second one is a MV cluster with 10 unpaired electrons largely delocalized over the 18 metal sites. A theoretical model that takes into account the interplay between electron transfer and magnetic exchange interactions is developed to explain the unexpected enhancement of the antiferromagnetic coupling when the number of unpaired electrons is reduced from 18 to 10 in these clusters. In the MV area, these systems represent the most complex magnetic clusters studied theoretically so far. Because of the high complexity of the systems, the number of relevant parameters is too large for a conventional model Hamiltonian approach. We therefore perform a theoretical study that combines ab initio calculations with the model Hamiltonian. In this way, we use ab initio calculations performed on small fragments of the cluster to lower the degrees of freedom of the parameter set of the model Hamiltonian that operates in the whole MV cluster. This approach shows the usefulness of combining ab initio calculations with model Hamiltonians in order to explore the magnetic properties of large and complex molecular systems, emphasizing the key role played by the electron transfer in these model magnetic materials.

  12. Valence states and possible charge ordering in LaCo1-x Rh x O3

    Science.gov (United States)

    Streltsov, Sergey V.; Gapontsev, Vladimir V.; Khomskii, Daniel I.

    2016-03-01

    An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co3+ in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh3+ led, surprisingly, to a rapid appearance of magnetism in LaCo1-x Rh x O3, even for small amounts of doping. Different explanations for this effect were proposed in the literature. To clarify the situation we carried out unbiased ab initio calculations of this system. We concluded that, in agreement with the original assumption of Li et al, but in contrast with later statements (Knizek et al 2012 Phys. Rev. B 85 134401), this effect is caused by the valence change (’redox reaction’) Co3+   +  Rh3+ \\to Co2+   +  Rh4+ , which creates magnetic Co2+ and Rh4+ ions. For the half-filled case LaCo1/2Rh1/2O3 we obtained the state with charge ordering of Co2+ and Rh4+ ions, which according to our calculations are antiferromagnetically coupled. The obtained results reasonably explain the observed behavior of the magnetic susceptibility of LaCo1-x Rh x O3, and the novel state predicted at half-doping could be verified experimentally by detailed structural and magnetic studies and by x-ray absorption spectroscopy.

  13. Valence states and possible charge ordering in LaCo(1-x)Rh(x)O₃.

    Science.gov (United States)

    Streltsov, Sergey V; Gapontsev, Vladimir V; Khomskii, Daniel I

    2016-03-02

    An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co(3+) in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh(3+) led, surprisingly, to a rapid appearance of magnetism in LaCo(1-x)Rh(x)O3, even for small amounts of doping. Different explanations for this effect were proposed in the literature. To clarify the situation we carried out unbiased ab initio calculations of this system. We concluded that, in agreement with the original assumption of Li et al, but in contrast with later statements (Knizek et al 2012 Phys. Rev. B 85 134401), this effect is caused by the valence change ('redox reaction') Co(3+) +  Rh(3+) → Co(2+) +  Rh(4+), which creates magnetic Co(2+) and Rh(4+) ions. For the half-filled case LaCo1/2Rh1/2O3 we obtained the state with charge ordering of Co(2+) and Rh(4+) ions, which according to our calculations are antiferromagnetically coupled. The obtained results reasonably explain the observed behavior of the magnetic susceptibility of LaCo(1-x)Rh(x)O3, and the novel state predicted at half-doping could be verified experimentally by detailed structural and magnetic studies and by x-ray absorption spectroscopy.

  14. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    Science.gov (United States)

    Wickramaratne, Darshana; Zahid, Ferdows; Lake, Roger K.

    2015-08-01

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a "Mexican hat" or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III-VI materials GaS, GaSe, InS, InSe, for Bi2Se3, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III-VI materials and Bi2Se3 is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

  15. Electronic and thermoelectric properties of van der Waals materials with ring-shaped valence bands

    Energy Technology Data Exchange (ETDEWEB)

    Wickramaratne, Darshana, E-mail: darshanaw@engineering.ucsb.edu, E-mail: rlake@ece.ucr.edu; Lake, Roger K., E-mail: darshanaw@engineering.ucsb.edu, E-mail: rlake@ece.ucr.edu [Laboratory for Terahertz and Terascale Electronics, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521 (United States); Zahid, Ferdows [Department of Physics and the Center of Theoretical and Computational Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China)

    2015-08-21

    The valence band of a variety of few-layer, two-dimensional materials consist of a ring of states in the Brillouin zone. The energy-momentum relation has the form of a “Mexican hat” or a Rashba dispersion. The two-dimensional density of states is singular at or near the band edge, and the band-edge density of modes turns on nearly abruptly as a step function. The large band-edge density of modes enhances the Seebeck coefficient, the power factor, and the thermoelectric figure of merit ZT. Electronic and thermoelectric properties are determined from ab initio calculations for few-layer III–VI materials GaS, GaSe, InS, InSe, for Bi{sub 2}Se{sub 3}, for monolayer Bi, and for bilayer graphene as a function of vertical field. The effect of interlayer coupling on these properties in few-layer III–VI materials and Bi{sub 2}Se{sub 3} is described. Analytical models provide insight into the layer dependent trends that are relatively consistent for all of these few-layer materials. Vertically biased bilayer graphene could serve as an experimental test-bed for measuring these effects.

  16. High-pressure synchrotron Mössbauer and X-ray diffraction studies: Exploring the structure-related valence fluctuation in EuNi2P2

    Science.gov (United States)

    Li, Chunyu; Yu, Zhenhai; Bi, Wenli; Zhao, Jiyong; Hu, Michael Y.; Zhao, Jinggeng; Wu, Wei; Luo, Jianlin; Yan, Hao; Alp, Esen E.; Liu, Haozhe

    2016-11-01

    The high-pressure effect on valence fluctuation of the ThCr2Si2-type intermetallic compound EuNi2P2 has been investigated using in situ synchrotron Mössbauer spectroscopy (SMS). The isomer shift of 151Eu in EuNi2P2 increases monotonically with increasing pressure up to 50 GPa, suggesting a valence transition of the Eu from mixed toward trivalent. The synchrotron angle-dispersive X-ray diffraction (AD-XRD) experiment shows that EuNi2P2 remains in the tetragonal structure up to 32.5 GPa at room temperature. We propose that the evolutions of bonding distance with pressure have an obvious effect on the valence fluctuation.

  17. Hydration of the cyanide ion: an ab initio quantum mechanical charge field molecular dynamics study.

    Science.gov (United States)

    Moin, Syed Tarique; Hofer, Thomas S

    2014-12-21

    This paper presents an ab initio quantum mechanical charge field molecular dynamics simulation study of the cyanide anion (CN(-)) in aqueous solution where hydrogen bond formation plays a dominant role in the hydration process. Preferential orientation of water hydrogens compared to oxygen atoms was quantified in terms of radial, angular as well as coordination number distributions. All structural results indicate that the water hydrogens are attracted towards CN(-) atoms, thus contributing to the formation of the hydration layer. Moreover, a clear picture of the local arrangement of water molecules around the ellipsoidal CN(-) ion is provided via angular-radial distribution and spatial distribution functions. Apart from the structural analysis, the evaluation of water dynamics in terms of ligand mean residence times and H-bond correlation functions indicates the weak structure making capacity of the CN(-) ion. The similar values of H-bond lifetimes obtained for the NHwat and CHwat bonds indicate an isokinetic behaviour of these H-bonds, since there is a very small difference in the magnitude of the lifetimes. On the other hand, the H-bond lifetimes between water molecules of the hydration shell, and between solute and solvent evidence the slightly stable hydration of the CN(-). Overall, the H-bonding dominates in the hydration process of the cyanide anion enabling it to become soluble in the aqueous environment associated to chemical and biological processes.

  18. Decarboxylation of furfural on Pd(111): Ab initio molecular dynamics simulations

    Science.gov (United States)

    Xue, Wenhua; Dang, Hongli; Shields, Darwin; Liu, Yingdi; Jentoft, Friederike; Resasco, Daniel; Wang, Sanwu

    2013-03-01

    Furfural conversion over metal catalysts plays an important role in the studies of biomass-derived feedstocks. We report ab initio molecular dynamics simulations for the decarboxylation process of furfural on the palladium surface at finite temperatures. We observed and analyzed the atomic-scale dynamics of furfural on the Pd(111) surface and the fluctuations of the bondlengths between the atoms in furfural. We found that the dominant bonding structure is the parallel structure in which the furfural plane, while slightly distorted, is parallel to the Pd surface. Analysis of the bondlength fluctuations indicates that the C-H bond is the aldehyde group of a furfural molecule is likely to be broken first, while the C =O bond has a tendency to be isolated as CO. Our results show that the reaction of decarbonylation dominates, consistent with the experimental measurements. Supported by DOE (DE-SC0004600). Simulations and calculations were performed on XSEDE's and NERSC's supercomputers.

  19. Character Disposition and Behavior Type: Influences of Valence on Preschool Children's Social Judgments

    Science.gov (United States)

    Jones, Elaine F.; Tobias, Marvin; Pauley, Danielle; Thomson, Nicole Renick; Johnson, Shawana Lewis

    2009-01-01

    The authors studied the influences of valence information on preschool children's (n = 47) moral (good or bad), liking (liked or disliked by a friend), and consequence-of-behavior (reward or punishment) judgments. The authors presented 8 scenarios describing the behavior valence, positive valence (help, share), negative valence (verbal insult,…

  20. Molecular potentials and wave function mapping by high-resolution electron spectroscopy and ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kimberg, Victor, E-mail: victor.kimberg@pks.mpi.de [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden (Germany); Miron, Catalin, E-mail: miron@synchrotron-soleil.fr [Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex (France)

    2014-08-15

    Highlights: • Some studies related to the vibrational wave functions mapping phenomenon are reviewed. • The core-excited vibrational wave functions were mapped using dissociative and bound final states. • High-resolution experimental data is accompanied by ab initio calculations. • The mapping phenomenon allows one to extract constants of the molecular potentials. • The mapping techniques are general and can be applied for the study of many systems. - Abstract: The recent development of high brightness 3{sup rd} generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle.

  1. Ab initio calculation of the potential bubble nucleus 34Si

    Science.gov (United States)

    Duguet, T.; Somà, V.; Lecluse, S.; Barbieri, C.; Navrátil, P.

    2017-03-01

    Background: The possibility that an unconventional depletion (referred to as a "bubble") occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which 34Si appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable 34Si is currently out of reach, (d ,p ) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1 /2--3 /2- splitting in the spectrum of 35Si as compared to 37S. Purpose: We study the potential bubble structure of 34Si on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of 34Si and 36S. In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in 36S. The next observable of interest is the low-lying spectroscopy of 35Si and 37S obtained from (d ,p ) experiments along with the spectroscopy of 33Al and 35P obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to

  2. Dissociable effects of valence and arousal in adaptive executive control.

    Directory of Open Access Journals (Sweden)

    Christof Kuhbandner

    Full Text Available BACKGROUND: Based on introspectionist, semantic, and psychophysiological experimental frameworks, it has long been assumed that all affective states derive from two independent basic dimensions, valence and arousal. However, until now, no study has investigated whether valence and arousal are also dissociable at the level of affect-related changes in cognitive processing. METHODOLOGY/PRINCIPAL FINDINGS: We examined how changes in both valence (negative vs. positive and arousal (low vs. high influence performance in tasks requiring executive control because recent research indicates that two dissociable cognitive components are involved in the regulation of task performance: amount of current control (i.e., strength of filtering goal-irrelevant signals and control adaptation (i.e., strength of maintaining current goals over time. Using a visual pop-out distractor task, we found that control is exclusively modulated by arousal because interference by goal-irrelevant signals was largest in high arousal states, independently of valence. By contrast, control adaptation is exclusively modulated by valence because the increase in control after trials in which goal-irrelevant signals were present was largest in negative states, independent of arousal. A Monte Carlo simulation revealed that differential effects of two experimental factors on control and control adaptation can be dissociated if there is no correlation between empirical interference and conflict-driven modulation of interference, which was the case in the present data. Consequently, the observed effects of valence and arousal on adaptive executive control are indeed dissociable. CONCLUSIONS/SIGNIFICANCE: These findings indicate that affective influences on cognitive processes can be driven by independent effects of variations in valence and arousal, which may resolve several heterogeneous findings observed in previous studies on affect-cognition interactions.

  3. Theoretical study of the interplay between lithium bond and hydrogen bond in complexes involved with HLi and HCN.

    Science.gov (United States)

    Li, Qingzhong; Hu, Ting; An, Xiulin; Li, Wenzuo; Cheng, Jianbo; Gong, Baoan; Sun, Jiazhong

    2009-12-21

    The lithium- and hydrogen-bonded complex of HLi-NCH-NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6-311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19% and 61% for the lithium and hydrogen bonds, respectively. A big cooperative energy (-5.50 kcal mol(-1)) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many-body interaction analysis has also been performed for HLi-(NCH)(N) (N=2-5) systems.

  4. Ab initio and density functional theory evidence on the rate-limiting step in the Morita-Baylis-Hillman reaction.

    Science.gov (United States)

    Roy, Dipankar; Sunoj, Raghavan B

    2007-11-08

    The first ab initio and DFT studies on the mechanism of the MBH reaction show that the rate-limiting step involves an intramolecular proton transfer in the zwitterionic intermediate generated by the addition of enolate to electrophile. The activation barrier for the C-C bond-formation is found to be 20.2 kcal/mol lower than the proton-transfer step for the MBH reaction between methyl vinyl ketone and benzaldehyde catalyzed by DABCO.

  5. Unusual H-Bond Topology and Bifurcated H-bonds in the 2-Fluoroethanol Trimer.

    Science.gov (United States)

    Thomas, Javix; Liu, Xunchen; Jäger, Wolfgang; Xu, Yunjie

    2015-09-28

    By using a combination of rotational spectroscopy and ab initio calculations, an unusual H-bond topology was revealed for the 2-fluoroethanol trimer. The trimer exhibits a strong heterochiral preference and adopts an open OH⋅⋅⋅OH H-bond topology while utilizing two types of bifurcated H-bonds involving organic fluorine. This is in stark contrast to the cyclic OH⋅⋅⋅OH H-bond topology adopted by trimers of water and other simple alcohols. The strengths of different H-bonds in the trimer were analyzed by using the quantum theory of atoms in molecules. The study showcases a remarkable example of a chirality-induced switch in H-bond topology in a simple transient chiral fluoroalcohol. It provides important insight into the H-bond topologies of small fluoroalcohol aggregates, which are proposed to play a key role in protein folding and in enantioselective reactions and separations where fluoroalcohols serve as a (co)solvent.

  6. Space-Valence Priming with Subliminal and Supraliminal Words

    Directory of Open Access Journals (Sweden)

    Ulrich eAnsorge

    2013-02-01

    Full Text Available To date it is unclear whether (1 awareness-independent non-evaluative semantic processes influence affective semantics and whether (2 awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked primes and visible targets in a space-valence across-category congruence effect. In line with (1, we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1: Classifications were faster with a congruent prime (e.g., the prime ‘up’ before the target ‘happy’ than with an incongruent prime (e.g., the prime ‘up’ before the target ‘sad’. In contrast to (2, no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2. Control conditions showed that standard masked response-priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1 that awareness-independent non-evaluative semantic priming influences valence judgments.

  7. The acoustic correlates of valence depend on emotion family.

    Science.gov (United States)

    Belyk, Michel; Brown, Steven

    2014-07-01

    The voice expresses a wide range of emotions through modulations of acoustic parameters such as frequency and amplitude. Although the acoustics of individual emotions are well understood, attempts to describe the acoustic correlates of broad emotional categories such as valence have yielded mixed results. In the present study, we analyzed the acoustics of emotional valence for different families of emotion. We divided emotional vocalizations into "motivational," "moral," and "aesthetic" families as defined by the OCC (Ortony, Clore, and Collins) model of emotion. Subjects viewed emotional scenarios and were cued to vocalize congruent exclamations in response to them, for example, "Yay!" and "Damn!". Positive valence was weakly associated with high-pitched and loud vocalizations. However, valence interacted with emotion family for both pitch and amplitude. A general acoustic code for valence does not hold across families of emotion, whereas family-specific codes provide a more accurate description of vocal emotions. These findings are consolidated into a set of "rules of expression" relating vocal dimensions to emotion dimensions.

  8. Social learning modulates the lateralization of emotional valence.

    Science.gov (United States)

    Shamay-Tsoory, Simone G; Lavidor, Michal; Aharon-Peretz, Judith

    2008-08-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by the right prefrontal cortex (PFC), whereas recognition of complex social emotions is processed preferentially by the left PFC. Experiment 1 assessed the ability of healthy controls and patients with right and left PFC lesions to recognize basic and complex emotions. Experiment 2 modeled the patient's data of Experiment 1 on healthy participants under lateralized displays of the emotional stimuli. Both experiments support the Type as well as the Valence Hypotheses. However, our findings indicate that the Valence Hypothesis holds for basic but less so for complex emotions. It is suggested that, since social learning overrules the basic preference of valence in the hemispheres, the processing of complex emotions in the hemispheres is less affected by valence.

  9. Effects of valence and divided attention on cognitive reappraisal processes.

    Science.gov (United States)

    Morris, John A; Leclerc, Christina M; Kensinger, Elizabeth A

    2014-12-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources.

  10. Oxygen Evolution at Manganite Perovskite Ruddlesden-Popper Type Particles: Trends of Activity on Structure, Valence and Covalence

    Directory of Open Access Journals (Sweden)

    Majid Ebrahimizadeh Abrishami

    2016-11-01

    Full Text Available An improved understanding of the correlation between the electronic properties of Mn-O bonds, activity and stability of electro-catalysts for the oxygen evolution reaction (OER is of great importance for an improved catalyst design. Here, an in-depth study of the relation between lattice structure, electronic properties and catalyst performance of the perovskite Ca1−xPrxMnO3 and the first-order RP-system Ca2−xPrxMnO4 at doping levels of x = 0, 0.25 and 0.5 is presented. Lattice structure is determined by X-ray powder diffraction and Rietveld refinement. X-ray absorption spectroscopy of Mn-L and O-K edges gives access to Mn valence and covalency of the Mn-O bond. Oxygen evolution activity and stability is measured by rotating ring disc electrode studies. We demonstrate that the highest activity and stability coincidences for systems with a Mn-valence state of +3.7, though also requiring that the covalency of the Mn-O bond has a relative minimum. This observation points to an oxygen evolution mechanism with high redox activity of Mn. Covalency should be large enough for facile electron transfer from adsorbed oxygen species to the MnO6 network; however, it should not be hampered by oxidation of the lattice oxygen, which might cause a crossover to material degradation. Since valence and covalency changes are not entirely independent, the introduction of the energy position of the eg↑ pre-edge peak in the O-K spectra as a new descriptor for oxygen evolution is suggested, leading to a volcano-like representation of the OER activity.

  11. Local Bonding Analysis of the Valence and Conduction Band Features of TiO2

    Science.gov (United States)

    2007-01-01

    anatase than with rutile .33 The shape of the L3 spectrum in Fig. 2 is also more qualitatively similar to XAS spectra of anatase surfaces shown in the...annealed TiO2 surfaces of anatase and rutile at photon ener- gies of 40–80 eV would appear to reveal a stronger similarity to the resonance behavior...of the anatase surfaces than to rutile , for which the Ti 3p→4sp resonance at 54 eV is dominant.7 However, it is clear from the same study that the CIS

  12. Hard-Core Bosons on the Kagome Lattice: Valence-Bond Solids and Their Quantum Melting

    Science.gov (United States)

    Isakov, S. V.; Wessel, S.; Melko, R. G.; Sengupta, K.; Kim, Yong Baek

    2006-10-01

    Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities ρ=1/3 and ρ=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid.

  13. Does fluorine participate in halogen bonding?

    Science.gov (United States)

    Eskandari, Kiamars; Lesani, Mina

    2015-03-16

    When R is sufficiently electron withdrawing, the fluorine in the R-F molecules could interact with electron donors (e.g., ammonia) and form a noncovalent bond (F⋅⋅⋅N). Although these interactions are usually categorized as halogen bonding, our studies show that there are fundamental differences between these interactions and halogen bonds. Although the anisotropic distribution of electronic charge around a halogen is responsible for halogen bond formations, the electronic charge around the fluorine in these molecules is spherical. According to source function analysis, F is the sink of electron density at the F⋅⋅⋅N BCP, whereas other halogens are the source. In contrast to halogen bonds, the F⋅⋅⋅N interactions cannot be regarded as lump-hole interactions; there is no hole in the valence shell charge concentration (VSCC) of fluorine. Although the quadruple moment of Cl and Br is mainly responsible for the existence of σ-holes, it is negligibly small in the fluorine. Here, the atomic dipole moment of F plays a stabilizing role in the formation of F⋅⋅⋅N bonds. Interacting quantum atoms (IQA) analysis indicates that the interaction between halogen and nitrogen in the halogen bonds is attractive, whereas it is repulsive in the F⋅⋅⋅N interactions. Virial-based atomic energies show that the fluorine, in contrast to Cl and Br, stabilize upon complex formation. According to these differences, it seems that the F⋅⋅⋅N interactions should be referred to as "fluorine bond" instead of halogen bond.

  14. Role of valence states of adsorbates in inelastic electron tunneling spectroscopy: A study of nitric oxide on Cu(110) and Cu(001)

    Science.gov (United States)

    Shiotari, Akitoshi; Okuyama, Hiroshi; Hatta, Shinichiro; Aruga, Tetsuya; Alducin, Maite; Frederiksen, Thomas

    2016-08-01

    We studied nitric oxide (NO) molecules on Cu(110) and Cu(001) surfaces with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). NO monomers on the surfaces are characterized by STM images reflecting 2 π* resonance states located at the Fermi level. NO is bonded vertically to the twofold short-bridge site on Cu(110) and to the fourfold hollow site on Cu(001). When NO molecules form dimers on the surfaces, the valence orbitals are modified due to the covalent bonding. We measured inelastic electron tunneling spectroscopy (IETS) for both NO monomers and dimers on the two surfaces, and detected characteristic structures assigned to frustrated rotation and translation modes by density functional theory simulations. Considering symmetries of valence orbitals and vibrational modes, we explain the intensity of the observed IETS signals in a qualitative manner.

  15. Bonding Energy and Growth Habit of Lithium Niobate Single Crystals

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    On the basis of crystallographic structure of lithium niobate (LN), the bonding energy was quantitatively calculated by the bond valence sum model, which was employed to investigate the crystal growth. A possible relationship between the crystal growth habit and chemical bonding energy of LN crystals are found. It is found that the higher the bond energy, the slower the growth rate, and the more important the plane. The analytical results indicate that (012) plane is the most influential face for the LN crystal growth, which consists well with the standard card (JCPDS Card: 20-0631) and our previous experimental observation. The current work shows that the chemical bond analysis of LN crystals allows us to predict its growth habit and thus to obtain the expected morphology during the spontaneous growth.

  16. Gradient Bundle Analysis: A Full Topological Approach to Chemical Bonding

    CERN Document Server

    Morgenstern, Amanda

    2016-01-01

    The "chemical bond" is a central concept in molecular sciences, but there is no consensus as to what a bond actually is. Therefore, a variety of bonding models have been developed, each defining the structure of molecules in a different manner with the goal of explaining and predicting chemical properties. This thesis describes the initial development of gradient bundle analysis (GBA), a chemical bonding model that creates a high resolution picture of chemical interactions within the charge density framework. GBA is based on concepts from the quantum theory of atoms in molecules (QTAIM), but uses a more complete picture of the topology and geometry of the electron charge density to understand and predict bonding interactions. Gradient bundles are defined as volumes bounded by zero-flux surfaces (ZFSs) in the gradient of the charge density with well-defined energies. The structure of gradient bundles provides an avenue for detecting the locations of valence electrons, which correspond to reactive regions in a ...

  17. Tautomeric preferences and electron delocalization in biurets, thiobiurets, and dithiobiurets: An ab initio study

    Science.gov (United States)

    Adane, Legesse; Bharatam, Prasad V.

    In several literature reports biuret and its sulfur analogs are reported to exist in their diketo form with general formula H2N bond CX bond NH bond CY bond NH2 (X = O, Y = O, biuret; X = Y = S, dithiobiuret; and X = O, Y = S, thiobiuret). On the other hand, recently reported results on the electronic structure of biguanide analogs (X = Y = NH)demonstrated that a form equivalent to diketo is not the preferred structure. Thus, a systematic ab initio study on the tautomeric preferences of biuret and its sulfur analogs (dithiobiuret and thiobiuret) has been carried out. The results indicate that an interplay of conjugative stabilization and intramolecular hydrogen bonding to play a role in tautomeric preferences. Energy and geometric parameters, natural bond orbital analyses have been employed to understand the chemistry of the title compounds. The results indicate that unlike biguanides, these compounds prefer diketo forms containing hydrogen on the bridging nitrogen (N4) and in a trans-arrangement (1a-4a). However, tautomerization of these keto forms to the corresponding enol isomers was also found to be highly probable.

  18. Orbital-free ab initio molecular dynamics study of the static structure and dynamic properties of the free liquid surface of Sn

    Directory of Open Access Journals (Sweden)

    del Rio B. G.

    2017-01-01

    Full Text Available We report results of an orbital-free ab initio molecular dynamics (OF-AIMD study of the free liquid surface (FLS of Sn at 1000 K and 600 K. A key ingredient in the OF-AIMD method is the local pseudopotential describing the ions-valence electrons interaction. We have used a force-matching method to derive a local pseudopotential suitable to account for the variation of the forces from the bulk to the FLS. We obtain very good results for structural properties, such as the reflectivity, including the characteristic shoulder it presents in x-ray experiments. Moreover we have been able to study ab initio for the first time the evolution in some dynamical properties as we move from the central region, where the system behaves like the bulk liquid, to the FLS.

  19. Orbital-free ab initio molecular dynamics study of the static structure and dynamic properties of the free liquid surface of Sn

    Science.gov (United States)

    del Rio, B. G.; González, L. E.

    2017-08-01

    We report results of an orbital-free ab initio molecular dynamics (OF-AIMD) study of the free liquid surface (FLS) of Sn at 1000 K and 600 K. A key ingredient in the OF-AIMD method is the local pseudopotential describing the ions-valence electrons interaction. We have used a force-matching method to derive a local pseudopotential suitable to account for the variation of the forces from the bulk to the FLS. We obtain very good results for structural properties, such as the reflectivity, including the characteristic shoulder it presents in x-ray experiments. Moreover we have been able to study ab initio for the first time the evolution in some dynamical properties as we move from the central region, where the system behaves like the bulk liquid, to the FLS.

  20. Ab initio Path Integral Molecular Dynamics Based on Fragment Molecular Orbital Method

    Science.gov (United States)

    Fujita, Takatoshi; Watanabe, Hirofumi; Tanaka, Shigenori

    2009-10-01

    We have developed an ab initio path integral molecular dynamics method based on the fragment molecular orbital method. This “FMO-PIMD” method can treat both nuclei and electrons quantum mechanically, and is useful to simulate large hydrogen-bonded systems with high accuracy. After a benchmark calculation for water monomer, water trimer and glycine pentamer have been studied using the FMO-PIMD method to investigate nuclear quantum effects on structure and molecular interactions. The applicability of the present approach is demonstrated through a number of test calculations.

  1. Graph theory meets ab initio molecular dynamics: atomic structures and transformations at the nanoscale.

    Science.gov (United States)

    Pietrucci, Fabio; Andreoni, Wanda

    2011-08-19

    Social permutation invariant coordinates are introduced describing the bond network around a given atom. They originate from the largest eigenvalue and the corresponding eigenvector of the contact matrix, are invariant under permutation of identical atoms, and bear a clear signature of an order-disorder transition. Once combined with ab initio metadynamics, these coordinates are shown to be a powerful tool for the discovery of low-energy isomers of molecules and nanoclusters as well as for a blind exploration of isomerization, association, and dissociation reactions.

  2. Detecting weak interactions between Au- and gas molecules: a photoelectron spectroscopic and ab initio study.

    Science.gov (United States)

    Gao, Yi; Huang, Wei; Woodford, Jeffrey; Wang, Lai-Sheng; Zeng, Xiao Cheng

    2009-07-15

    We show that anion photoelectron spectroscopy can be a very sensitive probe for weak intermolecular interactions between gold anion and a noble-gas atom or other nonreactive molecule. High-level ab initio calculations support the measured trend of relatively weak intermolecular interactions among various gold anion-atom complexes. The interaction between Au(-) and H(2)O is much stronger, comparable to a strong hydrogen bond. The interaction between Au(-) and O(2) is weaker than that between Au(-) and a noble-gas atom (Ar, Kr, or Xe).

  3. Ab initio Intermolecular Potential Energy Surface and Calculation of Second Virial Coefficients for the Cl2–Cl2 Dimer

    Directory of Open Access Journals (Sweden)

    Nguyen Thanh Duoc

    2015-12-01

    Full Text Available The results presented in this paper are the ab initio intermolecular potentials and the second virial coefficient, B2 (T of the dimer Cl2-Cl2. These ab initio potentials were proposed by the quantum chemical calculations at high level of theory CCSD (T with basis sets of Dunning’s valence correlation-consistent aug-cc-pVmZ (m = 2, 3; these results were extrapolated to complete basis set limit aug-cc-pV23Z. The ab initio energies of complete basis set limit aug-cc-pV23Z resulted from the exponential extrapolation were used to construct the 5-site pair potential functions. The second virial coefficients for this dimer were predicted from those with four-dimensional integration. The second virial coefficients were also corrected to first-order quantum effects. The results turn out to be in good agreement with experimental data, if available, or with those from empirical correlation. The quality of ab initio 5-site potentials proved the reliability for prediction of molecular thermodynamic properties.

  4. Physical properties of ternary silicide superconductors Li2XSi3 (X = Rh, Os): An ab initio study

    Science.gov (United States)

    Alam, M. A.; Zilani, M. A. K.; Parvin, F.; Hadi, M. A.

    2017-08-01

    An ab initio method, based on the plane wave pseudopotential and the generalized gradient approximation (GGA), is performed to investigate the physical properties such as structural, elastic, electronic and bonding properties of newly synthesized Li2RhSi3 and predicted Li2OsSi3 ternary silicide superconductors for the first time. Both of these compounds are mechanically stable and are brittle in nature. They also have good machinability. Electronic band structures reveal that these compounds have metallic characteristics. They possess complex bonding nature (metallic, covalent and ionic). According to theoretical Vickers hardness, Li2RhSi3 is softer than Li2OsSi3.

  5. Circulant Double Coverings of a Circulant Graph of Valency Five

    Institute of Scientific and Technical Information of China (English)

    Rong Quan FENG; Jin Ho KWAK

    2007-01-01

    Enumerating the isomorphism classes of several types of graph covering projections is one of the central research topics in enumerative topological graph theory. A covering of G is called circulant if its covering graph is circulant. Recently, the authors [Discrete Math., 277, 73-85 (2004)]enumerated the isomorphism classes of circulant double coverings of a certain type, called a typicalcovering, and showed that no double covering of a circulant graph of valency three is circulant. Also, in [Graphs and Combinatorics, 21, 386-400 (2005)], the isomorphism classes of circulant double coverings of a circulant graph of valency four are enumerated. In this paper, the isomorphism classes of circulant double coverings of a circulant graph of valency five are enumerated.

  6. Conduction Mechanism of Valence Change Resistive Switching Memory: A Survey

    Directory of Open Access Journals (Sweden)

    Ee Wah Lim

    2015-09-01

    Full Text Available Resistive switching effect in transition metal oxide (TMO based material is often associated with the valence change mechanism (VCM. Typical modeling of valence change resistive switching memory consists of three closely related phenomena, i.e., conductive filament (CF geometry evolution, conduction mechanism and temperature dynamic evolution. It is widely agreed that the electrochemical reduction-oxidation (redox process and oxygen vacancies migration plays an essential role in the CF forming and rupture process. However, the conduction mechanism of resistive switching memory varies considerably depending on the material used in the dielectric layer and selection of electrodes. Among the popular observations are the Poole-Frenkel emission, Schottky emission, space-charge-limited conduction (SCLC, trap-assisted tunneling (TAT and hopping conduction. In this article, we will conduct a survey on several published valence change resistive switching memories with a particular interest in the I-V characteristic and the corresponding conduction mechanism.

  7. Recognizing the emotional valence of names: an ERP study.

    Science.gov (United States)

    Wang, Lin; Zhu, Zude; Bastiaansen, Marcel; Hagoort, Peter; Yang, Yufang

    2013-04-01

    Unlike common nouns, person names refer to unique entities and generally have a referring function. We used event-related potentials to investigate the time course of identifying the emotional meaning of nouns and names. The emotional valence of names and nouns were manipulated separately. The results show early N1 effects in response to emotional valence only for nouns. This might reflect automatic attention directed towards emotional stimuli. The absence of such an effect for names supports the notion that the emotional meaning carried by names is accessed after word recognition and person identification. In addition, both names with negative valence and emotional nouns elicited late positive effects, which have been associated with evaluation of emotional significance. This positive effect started earlier for nouns than for names, but with similar durations. Our results suggest that distinct neural systems are involved in the retrieval of names' and nouns' emotional meaning.

  8. Ab initio design of CsSn(XxY 1−x3 (X and Y = Cl, Br, and I perovskites for photovoltaics

    Directory of Open Access Journals (Sweden)

    Arpan Krishna Deb

    2015-07-01

    Full Text Available Ab initio calculations on CsSnX3 perovskites and mixed halides CsSn(XxY 1−x3, X and Y = I, Cl, and Br, show that all of them have a direct band gap of ∼1 eV which can be tuned by varying the compositions of X and Y. The optimized supercells are tetragonal, orthorhombic or monoclinic. The top of the valence band arises from hybridization of Sn 4s and halogen p valence orbitals while the bottom of the conduction band has predominantly Sn p character. Similar to organo-metallic lead halides this is expected to facilitate p-p optical transitions that are highly favourable for photoabsorption. Our results suggest that these inorganic perovskites have the desired features to achieve high efficiency of photo-response with appropriate combination of halogens.

  9. Bonding in the Superionic Phase of Water

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, N; Fried, L E; Kuo, I W; Mundy, C J

    2005-02-07

    The predicted superionic phase of water is investigated via ab initio molecular dynamics at densities of 2.0-3.0 g/cc (34-115 GPa) along the 2000K isotherm. They find that extremely rapid (superionic) diffusion of protons occurs in a fluid phase at pressures between 34 and 58 GPa. A transition to a stable body-centered cubic (bcc) O lattice with superionic proton conductivity is observed between 70 and 75 GPa, a much higher pressure than suggested in prior work. They find that all molecular species at pressures greater than 75 GPa are too short lived to be classified as bound states. Up to 95 GPa, they find a solid superionic phase characterization by covalent O-H bonding. Above 95 GPa, a transient network phase is found characterized by symmetric O-H hydrogen bonding with nearly 50% covalent character. In addition, they describe a new metastable superionic phase with quenched O disorder.

  10. Lattice anomalies in CeNi unstable valence compound

    Energy Technology Data Exchange (ETDEWEB)

    Lazukov, V.N.; Nefeodova, E.V.; Alekseev, P.A.; Nemkovski, K.S.; Sadikov, I.P.; Tiden, N.N. [RRC ' ' Kurchatov Institute' ' , 123182 Moscow (Russian Federation); Sikolenko, V.V. [JINR, 141980 Dubna, Moscow region (Russian Federation); Staub, U.; Pradervand, C. [SLS, PSI, 5232 Villigen PSI (Switzerland); Braden, M. [LLB, CEA/Saclay, 91191 Gif sur Yvette Cedex (France); INFP Postfach 3640, 76021 Karlsruhe (Germany); Soderholm, L. [Chemistry Division, Argonne National Laboratory, Argonne Il-60439 (United States)

    2002-07-01

    Neutron diffraction and X-ray absorption measurements have been performed to study the changes in the structure and the Ce valence between 10 K and 295 K. No evidence for a phase transition was obtained, but some nearest-neighbour distances have clear peculiarities in the temperature range of 100 K to 150 K. The valence of Ce increases continuously with decreasing temperature, which can explain neither the lattice anomalies nor the previously observed temperature dependence of the phonon frequencies. A correlation between the gap-like magnetic excitation spectrum formed at low temperatures and observed lattice anomalies is discussed. (orig.)

  11. Diluted manganese on the bond-centered site in germanium

    CERN Document Server

    Decoster, S; Cottenier, S; Wahl, U; Correia, JG; Pereira, LMC; Lacasta, C; Da Silva, MR

    2010-01-01

    The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes.

  12. Indirect Interactions Between Proton Donors Separated by Several Hydrogen Bonds

    CERN Document Server

    Ogawa, Takaya; Tamaki, Takanori; Yamaguchi, Takeo

    2016-01-01

    We expand the definition of our recently proposed proton conduction mechanism, the packed-acid mechanism, which occurs under conditions of concentrated proton donors. The original definition stated that acid-acid interactions, which help overcome the barrier of the rate-determining step, occur only when a hydrogen bond is formed directly between proton donors. Here, it is shown that proton donors can interact with each other even when the donors are separated via several H-bonds. The effect of these interactions on proton diffusivity is confirmed by ab initio calculations.

  13. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    Science.gov (United States)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  14. Reciprocity Theorems for Ab Initio Force Calculations

    CERN Document Server

    Wei, C; Mele, E J; Rappe, A M; Lewis, Steven P.; Rappe, Andrew M.

    1996-01-01

    We present a method for calculating ab initio interatomic forces which scales quadratically with the size of the system and provides a physically transparent representation of the force in terms of the spatial variation of the electronic charge density. The method is based on a reciprocity theorem for evaluating an effective potential acting on a charged ion in the core of each atom. We illustrate the method with calculations for diatomic molecules.

  15. Discovering chemistry with an ab initio nanoreactor

    OpenAIRE

    Wang, Lee-Ping; Titov, Alexey; McGibbon, Robert; Liu, Fang; Pande, Vijay S.; Martínez, Todd J.

    2014-01-01

    Chemical understanding is driven by the experimental discovery of new compounds and reactivity, and is supported by theory and computation that provides detailed physical insight. While theoretical and computational studies have generally focused on specific processes or mechanistic hypotheses, recent methodological and computational advances harken the advent of their principal role in discovery. Here we report the development and application of the ab initio nanoreactor – a highly accelerat...

  16. First-principle study on bonding mechanism of ZnO by LDA+U method

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, G.C. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Sun, L.Z. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China) and National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: lzsun@xtu.edu.cn; Zhong, X.L. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China); Chen Xiaoshuang [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China)]. E-mail: xschen@mail.sitp.ac.cn; Wei Lu [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, 200083 Shanghai (China); Wang, J.B. [Key Laboratory of Low Dimensional Materials and Application Technology (Xiangtan University), Ministry of Education, Institute of Modern Physics, Xiangtan University, Xiangtan 411105 (China)]. E-mail: jbwang@xtu.edu.cn

    2007-08-13

    The electronic structure and the bonding mechanism of ZnO have been studied by using the Full-Potential Linear Augmented Plane Wave (FP-LAPW) method within the density-functional theory (DFT) based on LDA+U exchange correlation potential. The valence and the bonding charge density are calculated and compared with those derived from LDA and GGA to describe the bonding mechanism. The charge transfer along with the bonding process is analyzed by using the theory of Atoms in Molecules (AIM). The bonding, the topological characteristics and the p-d coupling effects on the bonding mechanism of ZnO are shown quantitatively with the critical points (CPs) along the bonding trajectory and the charge in the atomic basins. Meanwhile, the bonding characteristics for wurtzite, zinc blende and rocksalt phase of ZnO are discussed systematically in the present paper.

  17. Highly scalable Ab initio genomic motif identification

    KAUST Repository

    Marchand, Benoit

    2011-01-01

    We present results of scaling an ab initio motif family identification system, Dragon Motif Finder (DMF), to 65,536 processor cores of IBM Blue Gene/P. DMF seeks groups of mutually similar polynucleotide patterns within a set of genomic sequences and builds various motif families from them. Such information is of relevance to many problems in life sciences. Prior attempts to scale such ab initio motif-finding algorithms achieved limited success. We solve the scalability issues using a combination of mixed-mode MPI-OpenMP parallel programming, master-slave work assignment, multi-level workload distribution, multi-level MPI collectives, and serial optimizations. While the scalability of our algorithm was excellent (94% parallel efficiency on 65,536 cores relative to 256 cores on a modest-size problem), the final speedup with respect to the original serial code exceeded 250,000 when serial optimizations are included. This enabled us to carry out many large-scale ab initio motiffinding simulations in a few hours while the original serial code would have needed decades of execution time. Copyright 2011 ACM.

  18. Ab initio Bogoliubov coupled cluster theory

    Science.gov (United States)

    Signoracci, Angelo; Hagen, Gaute; Duguet, Thomas

    2014-09-01

    Coupled cluster (CC) theory has become a standard method in nuclear theory for realistic ab initio calculations of medium mass nuclei, but remains limited by its requirement of a Slater determinant reference state which reasonably approximates the nuclear system of interest. Extensions of the method, such as equation-of-motion CC, permit the calculation of nuclei with one or two nucleons added or removed from a doubly magic core, yet still only a few dozen nuclei are accessible with modern computational restrictions. In order to extend the applicability of ab initio methods to open-shell systems, the superfluid nature of nuclei must be taken into account. By utilizing Bogoliubov algebra and employing spontaneous symmetry breaking with respect to particle number conservation, superfluid systems can be treated by a single reference state. An ab initio theory to include correlations on top of a Bogoliubov reference state has been developed in the guise of standard CC theory. The formalism and first results of this Bogoliubov coupled cluster theory will be presented to demonstrate the applicability of the method.

  19. Mobile linkers on DNA-coated colloids: valency without patches.

    Science.gov (United States)

    Angioletti-Uberti, Stefano; Varilly, Patrick; Mognetti, Bortolo M; Frenkel, Daan

    2014-09-19

    Colloids coated with single-stranded DNA (ssDNA) can bind selectively to other colloids coated with complementary ssDNA. The fact that DNA-coated colloids (DNACCs) can bind to specific partners opens the prospect of making colloidal "molecules." However, in order to design DNACC-based molecules, we must be able to control the valency of the colloids, i.e., the number of partners to which a given DNACC can bind. One obvious, but not very simple approach is to decorate the colloidal surface with patches of single-stranded DNA that selectively bind those on other colloids. Here we propose a design principle that exploits many-body effects to control the valency of otherwise isotropic colloids. Using a combination of theory and simulation, we show that we can tune the valency of colloids coated with mobile ssDNA, simply by tuning the nonspecific repulsion between the particles. Our simulations show that the resulting effective interactions lead to low-valency colloids self-assembling in peculiar open structures, very different from those observed in DNACCs with immobile DNA linkers.

  20. Valence Induction with a Head-Lexicalized PCFG

    CERN Document Server

    Carroll, G; Carroll, Glenn; Rooth, Mats

    1998-01-01

    This paper presents an experiment in learning valences (subcategorization frames) from a 50 million word text corpus, based on a lexicalized probabilistic context free grammar. Distributions are estimated using a modified EM algorithm. We evaluate the acquired lexicon both by comparison with a dictionary and by entropy measures. Results show that our model produces highly accurate frame distributions.

  1. Prévalence et abondance de Charletonia cameroonensis Haitlinger ...

    African Journals Online (AJOL)

    Mots clés: Abondance, prévalence, C. cameroonensis, Z. variegatus, Zone côtière ... Kekeunou 2014 (Acari : Erythraeidae) in the coastal area of Cameroon. ... between the parasite abundance and the size of Z. variegatus population.

  2. Spin Dynamics and Magnetic Ordering in Mixed Valence Systems

    DEFF Research Database (Denmark)

    Shapiro, S. M.; Bjerrum Møller, Hans; Axe, J. D.

    1978-01-01

    Neutron scattering measurements are reported on the mixed valence compounds Ce//1// minus //xTh//x and TmSe. The chi double prime (Q, omega ) as derived from the inelastic spectra of Ce//0//. //7//4Th//0//. //2//6 shows a peak in the gamma phase near 20. 0 meV and shifts abruptly to greater than 70...

  3. Voice and Valency in San Luis Potosi Huasteco

    Science.gov (United States)

    Munoz Ledo Yanez, Veronica

    2014-01-01

    This thesis presents an analysis of the system of transitivity, voice and valency alternations in Huasteco of San Luis Potosi (Mayan) within a functional-typological framework. The study is based on spoken discourse and elicited data collected in the municipalities of Aquismon and Tancanhuitz de Santos in the state of San Luis Potosi, Mexico. The…

  4. Raman Sideband Cooling of Two-Valence-Electron Fermionic Atoms

    Institute of Scientific and Technical Information of China (English)

    LI Guo-Hui; XU Xin-Ye

    2011-01-01

    We propose a method for laser cooling two-valence-electron fermionic atoms. Our protocol employs resolved-sideband cooling on the stimulated Raman transition between the two magnetic sublevels (m = F and m = F - 1) of the ground state with total anguiar momentum F. The optical pumping from m = F - 1 to 1 Pi are used to decouple atoms in the m = F - 1 state. We calculate the Raman coupling generated by an engineered optical lattice. The result shows that it is possible to laser cool the two-valence-electron fermionic atoms to the ground state. The atoms in the ground state provide a new system for quantum optics.%@@ We propose a method for laser cooling two-valence-electron fermionic atoms.Our protocol employs resolved- sideband cooling on the stimulated Raman transition between the two magnetic sublevels (m=F and m = F- 1) of the ground state with total angular momentum F.The optical pumping from m = F - 1 to p are used to decouple atoms in the m = F - 1 state.We calculate the Raman coupling generated by an engineered optical lattice.The result shows that it is possible to laser cool the two-valence-electron fermionic atoms to the ground state.The atoms in the ground state provide a new system for quantum optics.

  5. "Plug-and-go" strategy to manipulate streptavidin valencies.

    Science.gov (United States)

    Sun, Xun; Montiel, Daniel; Li, Hao; Yang, Haw

    2014-08-20

    The streptavidin-biotin set is one of the most widely utilized conjugation pairs in biotechnological applications. The tetravalent nature of streptavidin and its homologues, however, tends to result in such undesirable complications as cross-linking or ill-defined stoichiometry. Here, we describe a mutagenesis-free strategy to manipulate the valencies of wild-type streptavidin that only requires commercially available reagents. The basic idea is simple: one obtains the desired streptavidin valency by blocking off unwanted binding sites using ancillary biotin ("plug"); this way, the extraordinary fM-biotin-binding affinity is fully retained for the remaining sites in streptavidin. In the present implementation, the ancillary biotin is attached to an auxiliary separation handle, negatively charged DNA or His-tagged protein, via a photochemically or enzymatically cleavable linker. Mixing streptavidin with the ancillary biotin construct produces a distribution of streptavidin valencies. The subsequent chromatographic separation readily isolates the construct of desired streptavidin valency, and the auxiliary handles are easily removed afterward ("go"). We demonstrate how this "plug-and-go" strategy allows a precise control for the compositions of streptavidin-biotin conjugates at the single-molecule level. This low-entry-barrier protocol could further expand the application scope of the streptavidin technology.

  6. Contrastive Verb Valency and Conceptual Structures in the Verbal Lexicon.

    Science.gov (United States)

    Devos, Filip; And Others

    1996-01-01

    Reports on research consisting of compiling a contrastive verb valency dictionary of Dutch, French, and English whose main strength lies in depicting semantic differences between its entries and conceptual differences between languages. Using these analyses, one can start to discern nuclear and peripheral meanings, analyze possible meaning…

  7. Valence shell charge concentration (VSCC) evolution: a tool to investigate the transformations within a VSCC throughout a chemical reaction.

    Science.gov (United States)

    Cortés-Guzmán, Fernando; Gómez, Rosa María; Rocha-Rinza, Tomas; Sánchez-Obregón, María Azucena; Guevara-Vela, José Manuel

    2011-11-17

    Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products. Recently, our group proposed the structural evolution, which has provided insights about the molecular structure changes occurring along a reaction path. Structural evolution may be defined as the development of a chemical reaction system across the partitioning of the nuclear configuration space into a finite number of structural regions defined on account of the topology of a scalar field, e.g., the electron density. In this paper, we present a tool to investigate within the framework of the Quantum Theory of Atoms in Molecules the evolvement of the Valence Shell Charge Concentration, the VSCC evolution, which is the description of the changes of electron density concentrations and depletions around the bonding area of an atom. The VSCC evolution provides supplementary information to the structural evolution because it allows the analysis of valence shells within a structural region, i.e., a subset of R(Q) with the same connectivity among the atoms forming a molecule. This new approach constitutes also a complement to the Valence-Shell Electron Pair Repulsion (VSEPR) model because it gives an account of the adjustments of electron pairs in the valence shell of an atom across a chemical reaction. The insertion reaction in the hydroformylation reaction of ethylene, the reduction of cyclohexanone with lithium aluminum hydride, the oxidation of methanol with chlorochromate, and the bimolecular nucleophilic substitution of CH(3)F with F(-) are used as representatives examples of the application of the VSCC evolution. Overall, this paper shows how the VSCC evolution through an analysis of the modifications of local charge concentrations and depletions in individual steps of a chemical reaction gives new insights about these processes.

  8. Local structure analysis in ab initio liquid water

    Science.gov (United States)

    Santra, Biswajit; DiStasio, Robert A., Jr.; Martelli, Fausto; Car, Roberto

    2015-09-01

    Within the framework of density functional theory, the inclusion of exact exchange and non-local van der Waals/dispersion (vdW) interactions is crucial for predicting a microscopic structure of ambient liquid water that quantitatively agrees with experiment. In this work, we have used the local structure index (LSI) order parameter to analyse the local structure in such highly accurate ab initio liquid water. At ambient conditions, the LSI probability distribution, P(I ), was unimodal with most water molecules characterised by more disordered high-density-like local environments. With thermal excitations removed, the resultant bimodal P(I ) in the inherent potential energy surface (IPES) exhibited a 3:1 ratio between high-density- and low-density-like molecules, with the latter forming small connected clusters amid the predominant population. By considering the spatial correlations and hydrogen bond network topologies among water molecules with the same LSI identities, we demonstrate that the signatures of the experimentally observed low- and high-density amorphous phases of ice are present in the IPES of ambient liquid water. Analysis of the LSI autocorrelation function uncovered a persistence time of ∼ 4 ps - a finding consistent with the fact that natural thermal fluctuations are responsible for transitions between these distinct yet transient local aqueous environments in ambient liquid water.

  9. LETTER TO THE EDITOR: Electronic structure and bonding properties in layered ternary carbide Ti3SiC2

    Science.gov (United States)

    Zhou, Yanchun; Sun, Zhimei

    2000-07-01

    Ab initio calculations based on the density-functional pseudopotential approach have been used to study the electronic structure and chemical bonding in layered machinable Ti3SiC2 ceramic. The calculations reveal that all three types of bonding - metallic, covalent and ionic - contribute to the bonding in Ti3SiC2. The high electric conductivity is attributed to the metallic bonding parallel to the basal plane and the high modulus and high melting point are attributed to the strong Ti-C-Ti-C-Ti covalent bond chains in the structure.

  10. Structural and Electronic Properties of Polyoxovanadoborates Containing the [V12B18O60] Core in Different Mixed Valence States

    Directory of Open Access Journals (Sweden)

    Patricio Hermosilla-Ibáñez

    2015-07-01

    Full Text Available This review summarizes all published data until April 2015 related to crystalline lattices formed by the [V12B18O60] core, which generates polyanionic clusters with different degrees of protonation and mixed-valence ratios. The negative charge of this cluster is counterbalanced by different cations such as protonated amines, hydronium, and alkaline, and transition metal ions. The cluster is shown to form extended 1D, 2D, or 3D frameworks by forming covalent bonds or presenting hydrogen bond interactions with the present secondary cations. These cations have little influence on the solid state reflectance UV-visible spectra of the polyanionic cluster, but are shown to modify the FT-IR spectra and the magnetic behavior of the different reported species.

  11. Understanding Bonds - Denmark

    DEFF Research Database (Denmark)

    Rimmer, Nina Røhr

    2016-01-01

    a specified rate of interest during the life of the bond and to repay the face value of the bond (the principal) when it “matures,” or comes due. Among the types of bonds you can choose from are: Government securities, municipal bonds, corporate bonds, mortgage and asset-backed securities, federal agency...

  12. Hydrogen Bonds and Vibrations of Water on (110) Rutile

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Nitin [ORNL; Neogi, Sanghamitra [Pennsylvania State University; Kent, Paul R [ORNL; Bandura, Andrei V. [St. Petersburg State University, St. Petersburg, Russia; Wesolowski, David J [ORNL; Cole, David R [ORNL; Sofo, Jorge O. [Pennsylvania State University

    2009-01-01

    We study the relation between hydrogen bonding and the vibrational frequency spectra of water on the (110) surface of rutile (α-TiO2) with three structural layers of adsorbed water. Using ab-initio molecular dynamics simulations at 280, 300 and 320K, we find strong, crystallographically-controlled adsorption sites, in general agreement with synchrotron X-ray and classical MD simulations. We demonstrate that these sites are produced by strong hydrogen bonds formed between the surface oxygen atoms and sorbed water molecules. The strength of these bonds is manifested by substantial broadening of the stretching mode vibrational band. The overall vibrational spectrum obtained from our simulations is in good agreement with inelastic neutron scattering experiments. We correlate the vibrational spectrum with different bonds at the surface in order to transform these vibrational measurements into a spectroscopy of surface interactions.

  13. Single-electron aerogen bonds: Do they exist?

    Science.gov (United States)

    Esrafili, Mehdi D.; Mohammadian-Sabet, Fariba; Solimannejad, Mohammad

    2016-08-01

    A novel type of σ-hole interaction is characterized between some noble gas containing molecules (KrOF2, KrO3, XeOF2 and XeO3) and methyl (CH3) or ethyl (C2H5) radical by means of ab initio calculations. This interaction is named as single-electron aerogen bond (SEAB), in view of the concepts of aerogen bond and single-electron bond interactions. The properties of SEABs are studied by molecular electrostatic potential, quantum theory of atom in molecules, natural bonding orbital and noncovalent interaction index analyses. The formation of an O⋯H interaction tends to increase the strength of the SEAB, when they coexist in a ternary complex.

  14. Interplay of I-TASSER and QUARK for template-based and ab initio protein structure prediction in CASP10.

    Science.gov (United States)

    Zhang, Yang

    2014-02-01

    We develop and test a new pipeline in CASP10 to predict protein structures based on an interplay of I-TASSER and QUARK for both free-modeling (FM) and template-based modeling (TBM) targets. The most noteworthy observation is that sorting through the threading template pool using the QUARK-based ab initio models as probes allows the detection of distant-homology templates which might be ignored by the traditional sequence profile-based threading alignment algorithms. Further template assembly refinement by I-TASSER resulted in successful folding of two medium-sized FM targets with >150 residues. For TBM, the multiple threading alignments from LOMETS are, for the first time, incorporated into the ab initio QUARK simulations, which were further refined by I-TASSER assembly refinement. Compared with the traditional threading assembly refinement procedures, the inclusion of the threading-constrained ab initio folding models can consistently improve the quality of the full-length models as assessed by the GDT-HA and hydrogen-bonding scores. Despite the success, significant challenges still exist in domain boundary prediction and consistent folding of medium-size proteins (especially beta-proteins) for nonhomologous targets. Further developments of sensitive fold-recognition and ab initio folding methods are critical for solving these problems. Copyright © 2013 Wiley Periodicals, Inc.

  15. Quantum wavepacket ab initio molecular dynamics: an approach for computing dynamically averaged vibrational spectra including critical nuclear quantum effects.

    Science.gov (United States)

    Sumner, Isaiah; Iyengar, Srinivasan S

    2007-10-18

    We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.

  16. Ab initio intermolecular potential energy surface of He-LiH

    Institute of Scientific and Technical Information of China (English)

    鄢国森; 杨明晖; 谢代前

    1997-01-01

    The intermolecular potential energy surface of He-LiH complex was studied using the full-electronic complete forth-order Miller-Plesset perturbation (MPPT) method.In ab initio calculations,the bond length of LiH was fixed at 0 159 5 nm.The potential has two local minima of Vm=-179.93 cm for the linear He LiH geormetrv at Rm=0.227 nm and Vm=-10.44 cm-1 for the linear He-HL1 geometry at Rm=0.516 nm The potemal exhibits strong anisotropy The analytic potential function with 31 parameters was determined by fitting to the calculated ab,mtio potentials The influence of variation of LiH bond length on the potential energy surface was also studied

  17. reaxFF Reactive Force Field for Disulfide Mechanochemistry, Fitted to Multireference ab Initio Data.

    Science.gov (United States)

    Müller, Julian; Hartke, Bernd

    2016-08-09

    Mechanochemistry, in particular in the form of single-molecule atomic force microscopy experiments, is difficult to model theoretically, for two reasons: Covalent bond breaking is not captured accurately by single-determinant, single-reference quantum chemistry methods, and experimental times of milliseconds or longer are hard to simulate with any approach. Reactive force fields have the potential to alleviate both problems, as demonstrated in this work: Using nondeterministic global parameter optimization by evolutionary algorithms, we have fitted a reaxFF force field to high-level multireference ab initio data for disulfides. The resulting force field can be used to reliably model large, multifunctional mechanochemistry units with disulfide bonds as designed breaking points. Explorative calculations show that a significant part of the time scale gap between AFM experiments and dynamical simulations can be bridged with this approach.

  18. Ab initio atomic recombination reaction energetics on model heat shield surfaces

    Science.gov (United States)

    Senese, Fredrick; Ake, Robert

    1992-01-01

    Ab initio quantum mechanical calculations on small hydration complexes involving the nitrate anion are reported. The self-consistent field method with accurate basis sets has been applied to compute completely optimized equilibrium geometries, vibrational frequencies, thermochemical parameters, and stable site labilities of complexes involving 1, 2, and 3 waters. The most stable geometries in the first hydration shell involve in-plane waters bridging pairs of nitrate oxygens with two equal and bent hydrogen bonds. A second extremely labile local minimum involves out-of-plane waters with a single hydrogen bond and lies about 2 kcal/mol higher. The potential in the region of the second minimum is extremely flat and qualitatively sensitive to changes in the basis set; it does not correspond to a true equilibrium structure.

  19. Puzzles in bonding and spectroscopy: the case of dicarbon.

    Science.gov (United States)

    Macrae, Roderick M

    2016-01-01

    The unstable molecule C₂ has been of interest since its identification as the source of the "Swan band" features observable in the spectra offlames, carbon arcs, white dwarf stars, and comets, and it continues to serve as a focal point for experimental and theoretical discovery. Recent spectroscopic work has identified a quintet state of the molecule for the first time, while new insights into the bond order of C₂ in its ground state have been provided by sophisticated computational methods based on valence bond theory. This article gives a review of spectroscopic and computational work on C₂ including both historical background and the most recent discoveries.

  20. Paradigms and Plastic Facts in the History of Valence.

    Science.gov (United States)

    Zavaleta, David

    1988-01-01

    Traces the development of bonding theory and notes the influence of preconceived theory upon this development. Considers ideas of alchemy, Newton, Dalton, Lewis, and quantum mechanics. Suggests a move away from conservative descriptive approaches of bonding theory. (ML)

  1. Bonding and Moessbauer Isomer Shifts in (Hg,Pb)—1223 Cuprate

    Institute of Scientific and Technical Information of China (English)

    高发明; 田永君; 谌岩; 李东春; 董海峰; 张思远

    2003-01-01

    By using the chemical bond theory of dielectric description,the chemical bond parameters of(Hg,Pb)-1223 were calculated.The results show that the(Ba,Sr)-O and Ca-0 types of bond have higher ionic character,while the Cu-O and(Hg,Pb)-0 types of bond have more covalent character.Moessbauer isomer shifts of 57Fe and 119Sn doped in(Hg,Pb)-1223 were calculated by using the chemical environmental factor,he,defined by covalency and electronic polarizability.Four valence state tin and three valence iron sites were identified in 57Fe and 119Sn doped(Hg,Pb)-1223 superconductor.It can be concluded that all of the Fe atoms substitute the Cu at square planar Cu(1) site,Whereas Sn prefers to substitute the square pyramidal Cu(2) site.

  2. Bonding and M?ssbauer Isomer Shifts in (Tl,Pb) - 1223 Cuprate

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    By using the chemical bond theory of dielectric description,the chemical bond parameters of (Tl,Pb) - 1223 was calculated.The results show that the Sr-O,Tl-O,and Ca-O types of bond have higher ionic character and the Cu-O types of bond have more covalent character.M?ssbauer isomer shifts of 57Fe and 119Sn doped in (Tl,Pb) -1223 were calculated by using the chemical environmental factor,he,defined by covalency and electronic polarizability.Four valence state tin and three valence iron sites were identified in 57Fe,and 119Sn doped (Tl,Pb) -1223 superconductor.We conclude that all of the Fe atoms substitute the Cu at square planar Cu (1) site,whereas Sn prefers to substitute the square pyramidal Cu (2) site.

  3. Embedding parameters in ab initio theory to develop approximations based on molecular similarity

    CERN Document Server

    Tanha, Matteus; Kaul, Shiva; Cappiello, Alexander; Gordon, Geoffrey J; Yaron, David J

    2015-01-01

    A means to take advantage of molecular similarity to lower the computational cost of electronic structure theory is explored, in which parameters are embedded into a low-cost, low-level (LL) ab initio model and adjusted to obtain agreement with results from a higher-level (HL) ab initio model. A parametrized LL (pLL) model is created by multiplying selected matrix elements of the Hamiltonian operators by scaling factors that depend on element types. Various schemes for applying the scaling factors are compared, along with the impact of making the scaling factors linear functions of variables related to bond lengths, atomic charges, and bond orders. The models are trained on ethane and ethylene, substituted with -NH2, -OH and -F, and tested on substituted propane, propylene and t-butane. Training and test datasets are created by distorting the molecular geometries and applying uniform electric fields. The fitted properties include changes in total energy arising from geometric distortions or applied fields, an...

  4. Embedding parameters in ab initio theory to develop well-controlled approximations based on molecular similarity

    CERN Document Server

    Tanha, Matteus; Cappiello, Alex; Gordon, Geoffrey J; Yaron, David J

    2013-01-01

    A means to take advantage of molecular similarity to lower the computational cost of electronic structure theory is proposed, in which parameters are embedded into a low-cost, low-level (LL) ab initio theory and adjusted to obtain agreement with a higher level (HL) ab initio theory. This approach is explored by training such a model on data for ethane and testing the resulting model on methane, propane and butane. The electronic distribution of the molecules is varied by placing them in strong electrostatic environments consisting of random charges placed on the corners of a cube. The results find that parameters embedded in HF/STO-3G theory can be adjusted to obtain agreement, to within about 2 kcal/mol, with results of HF/6-31G theory. Obtaining this level of agreement requires the use of parameters that are functions of the bond lengths, atomic charges, and bond orders within the molecules. The argument is made that this approach provides a well-controlled means to take advantage of molecular similarity in...

  5. Electronic parameters of Sr2Nb2O7 and chemical bonding

    DEFF Research Database (Denmark)

    Atuchin, V.V.; Grivel, Jean-Claude; Korotkov, A.S.

    2008-01-01

    /2)) and Delta(O-Sr) = BE(O 1s)-BE(Sr 3d(5/2)), were used to characterize the valence electron transfer on the formation of the Nb-O and Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr2Nb2O7 and earlier published structural and XPS data for other Sr- or Nb...

  6. The quantum nature of the hydrogen bond: insight from path-integral molecular dynamics

    Science.gov (United States)

    Walker, Brent; Li, Xin-Zheng; Michaelides, Angelos

    2011-03-01

    Hydrogen (H) bonds are weak, generally intermolecular bonds, that hold together much of soft matter, the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of H means H-bonds are inherently quantum mechanical; effects such as zero point motion and tunneling should be considered, although often are not. In particular, a consistent picture of quantum nuclear effects on the strength of H-bonds and consequently the structure of H-bonded systems is still absent. Here, we report ab initio path-integral molecular dynamics studies on the quantum nature of the H-bond. Systematic examination of a range of H-bonded systems shows that quantum nuclei weaken weak H-bonds but strengthen relatively strong ones. This correlation arises from a competition between anharmonic intermolecular bond bending and intramolecular bond stretching. A simple rule of thumb enables predictions to be made for H-bonded bonded materials in general with merely classical knowledge (e.g. H-bond strength or H-bond length). Our work rationalizes the contrasting influence of quantum nuclear dynamics on a wide variety of materials, including liquid water and HF, and highlights the need for flexible molecules in force-field based studies of quantum nuclear dynamics.

  7. Cross Shear Roll Bonding

    DEFF Research Database (Denmark)

    Bay, Niels; Bjerregaard, Henrik; Petersen, Søren. B;

    1994-01-01

    The present paper describes an investigation of roll bonding an AlZn alloy to mild steel. Application of cross shear roll bonding, where the two equal sized rolls run with different peripheral speed, is shown to give better bond strength than conventional roll bonding. Improvements of up to 20......-23% in bond strength are found and full bond strength is obtained at a reduction of 50% whereas 65% is required in case of conventional roll bonding. Pseudo cross shear roll bonding, where the cross shear effect is obtained by running two equal sized rolls with different speed, gives the same results....

  8. Ab initio molecular crystal structures, spectra, and phase diagrams.

    Science.gov (United States)

    Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni

    2014-09-16

    Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling

  9. X-ray absorption near-edge structure and valence state of Mn in (Ga,Mn)N

    Science.gov (United States)

    Titov, A.; Biquard, X.; Halley, D.; Kuroda, S.; Bellet-Amalric, E.; Mariette, H.; Cibert, J.; Merad, A. E.; Merad, G.; Kanoun, M. B.; Kulatov, E.; Uspenskii, Yu. A.

    2005-09-01

    The band structure of the diluted magnetic semiconductor (Ga,Mn)N, and the x-ray absorption near-edge structure (XANES) at the K edge of Mn, were calculated using the linearized augmented plane wave method. The calculated K-edge spectra fit well with experimental data obtained on samples of Ga1-xMnxN with a wide range of Mn content, from x=0.3% to 5.7%. These samples were grown by molecular beam epitaxy. X-ray diffraction measurements and extended x-ray absorption fine structure studies were used to confirm the wurtzite structure of the samples, the absence of any secondary phase, and the substitutional position of Mn in the gallium sublattice of GaN. The shape of the measured XANES spectra does not depend on the Mn content, implying the same valence state and local atomic structure around the Mn atom in all samples. The comparison between the measured spectra and the results of the ab initio calculation offers a clear interpretation of the preedge structure: It is mainly due to dipolar transitions, with a single peak in the case of Mn2+ and an additional peak for Mn3+ . Such a behavior of the XANES preedge of Mn2+ was confirmed experimentally on (Ga,Mn)As and (Zn,Mn)Te. We conclude that the valence state of Mn in wurtzite (Ga,Mn)N is 3+ , a conclusion which is also supported by infrared optical transmission and magnetization data obtained on the same samples.

  10. Work Valence as a Predictor of Academic Achievement in the Family Context

    Science.gov (United States)

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    This study asserts a theoretical model of academic and work socialization within the family setting. The presumed associations between parents' work valences, children's work valences and valence perceptions, and children's academic interest and achievement are tested. The results suggest that children's perceptions of parents…

  11. Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal

    Science.gov (United States)

    Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

    2010-01-01

    Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can…

  12. Electronic structure of AlCrN films investigated using various photoelectron spectroscopies and ab initio calculations

    Science.gov (United States)

    Tatemizo, N.; Imada, S.; Miura, Y.; Yamane, H.; Tanaka, K.

    2017-03-01

    The valence band (VB) structures of wurtzite AlCrN (Cr concentration: 0-17.1%), which show optical absorption in the ultraviolet-visible-infrared light region, were investigated via photoelectron yield spectroscopy (PYS), x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), and ab initio density of states (DOS) calculations. An obvious photoelectron emission threshold was observed ~5.3 eV from the vacuum level for AlCrN, whereas no emission was observed for AlN in the PYS spectra. Comparisons of XPS and UPS VB spectra and the calculated DOS imply that Cr 3d states are formed both at the top of the VB and in the AlN gap. These data suggest that Cr doping could be a viable option to produce new materials with relevant energy band structures for solar photoelectric conversion.

  13. Recent advances in electronic structure theory and their influence on the accuracy of ab initio potential energy surfaces

    Science.gov (United States)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1989-01-01

    Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F + H2 yields HF + H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces.

  14. Wire bonding in microelectronics

    CERN Document Server

    Harman, George G

    2010-01-01

    Wire Bonding in Microelectronics, Third Edition, has been thoroughly revised to help you meet the challenges of today's small-scale and fine-pitch microelectronics. This authoritative guide covers every aspect of designing, manufacturing, and evaluating wire bonds engineered with cutting-edge techniques. In addition to gaining a full grasp of bonding technology, you'll learn how to create reliable bonds at exceedingly high yields, test wire bonds, solve common bonding problems, implement molecular cleaning methods, and much more. Coverage includes: Ultrasonic bonding systems and technologies, including high-frequency systems Bonding wire metallurgy and characteristics, including copper wire Wire bond testing Gold-aluminum intermetallic compounds and other interface reactions Gold and nickel-based bond pad plating materials and problems Cleaning to improve bondability and reliability Mechanical problems in wire bonding High-yield, fine-pitch, specialized-looping, soft-substrate, and extreme-temperature wire bo...

  15. X-ray Emission Spectroscopy to Study Ligand Valence Orbitals in Mn Coordination Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Smolentsev, Grigory; Soldatov, Alexander V; Messinger, Johannes; Merz, Kathrin; Weyhermuller, Thomas; Bergmann, Uwe; Pushkar, Yulia; Yano, Junko; Yachandra, Vittal K.; Glatzel, Pieter

    2009-03-02

    We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, [Mn(H2O)5NH2]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.

  16. On valence electron density, energy dissipation and plasticity of bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Pang, J.J.; Tan, M.J. [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798 Singapore (Singapore); Liew, K.M., E-mail: kmliew@cityu.edu.hk [Department of Civil and Architectural Engineering, City University of Hong Kong, Kowloon (Hong Kong)

    2013-11-15

    Highlights: ► Relationship between valence electron density and plasticity of metallic glasses. ► Poisson's ratio increases as electron density decreases. ► Energy dissipation proposed to understand plasticity. ► Low electron density indicates small activation energy. -- Abstract: In conventional crystalline alloys, valence electron density (VED) is one of the most significant factors in determining their phase stability and mechanical properties. Extending the concept to metallic glasses (MGs), it is found, not totally surprisingly, that their mechanical properties are VED-dependent as in crystalline alloys. Interestingly, the whole VED region can be separated into two zones: Zone 1 consists of Mg-, Ca-, and RE-based (RE for rare earth) alloys; Zone 2 consists of the rest of MGs. In either zone, for each type of MGs, Poisson's ratio generally decreases as VED increases. From the energy dissipation viewpoint proposed recently, the amorphous plasticity is closely related to the activation energy for the operation of shear-transformation-zones (STZs). Smaller STZ activation energy suggests higher ductility because STZs with lower activation energy are able to convert deformation work more efficiently into configurational energy rather than heat, which yields mechanical softening and advances the growth of shear bands (SBs). Following this model, it is revealed that the activation energies for STZ operation and crystallization are certainly proportional to VED. Thus, it is understood that, in Zone 2, MGs have a smaller VED and hence lower activation energies which are favorable for ductility and Poisson's ratio. In Zone 1, MGs have the lowest VED but apparent brittleness because either of low glass transition temperature and poor resistance to oxidation or of a large fraction of covalent bonds.

  17. Hydrogen bonding in oxalic acid and its complexes: A database study of neutron structures

    Indian Academy of Sciences (India)

    R Chitra; Amit Das; R R Choudhury; M Ramanadham; R Chidambaram

    2004-08-01

    The basic result of carboxylic group that the oxygen atom of the –OH never seems to be a hydrogen bond acceptor is violated in the cases, namely urea oxalic acid and bis urea oxalic acid complexes, where the hydroxyl oxygen atom is an acceptor of a weak N–H... O hydrogen bond. The parameters of this hydrogen bond, respectively in these structures are: hydrogen acceptor distance 2.110 Å and 2.127 Å and the bending angle at hydrogen, 165.6° and 165.8°. The bond strength around the hydroxyl oxygen is close to 1.91 valence units, indicating that it has hardly any strength left to form hydrogen bonds. These two structures being highly planar, force the formation of this hydrogen bond. As oxalic acid is the common moiety, the structures of the two polymorphs, -oxalic acid and -oxalic acid, also were looked into in terms of hydrogen bonding and packing.

  18. Investigating the quartz (1010)/water interface using classical and ab initio molecular dynamics.

    Science.gov (United States)

    Skelton, A A; Wesolowski, D J; Cummings, P T

    2011-07-19

    Two different terminations of the (1010) surface of quartz (α and β) interacting with water are simulated by classical (CMD) (using two different force fields) and ab initio molecular dynamics (AIMD) and compared with previously published X-ray reflectivity (XR) experiments. Radial distribution functions between hydroxyl and water show good agreement between AIMD and CMD using the ClayFF force field for both terminations. The Lopes et al. (Lopes, P. E. M.; Murashov, V.; Tazi, M.; Demchuk, E.; MacKerell, A. D. J. Phys. Chem. B2006, 110, 2782-2792) force field (LFF), however, underestimates the extent of hydroxyl-water hydrogen bonding. The β termination is found to contain hydroxyl-hydroxyl hydrogen bonds; the quartz surface hydroxyl hydrogens and oxygens that hydrogen bond with each other exhibit greatly reduced hydrogen bonding to water. Conversely, the hydroxyl hydrogen and oxygens that are not hydrogen bonded to other surface hydroxyls but are connected to those that are show a considerable amount of hydrogen bonding to water. The electron density distribution of an annealed surface of quartz (1010) obtained by XR is in qualitative agreement with electron densities calculated by CMD and AIMD. In all simulation methods, the interfacial water peak appears farther from the surface than observed by XR. Agreement among AIMD, LFF, and XR is observed for the relaxation of the near-surface atoms; however, ClayFF shows a larger discrepancy. Overall, results show that for both terminations of (1010), LFF treats the near-surface structure more accurately whereas ClayFF treats the interfacial water structure more accurately. It is shown that the number of hydroxyl and water hydrogen bonds to the bridging Si-O-Si oxygens connecting the surface silica groups to the rest of the crystal is much greater for the α than the β termination. It is suggested that this may play a role in the greater resistance to dissolution of the β termination than that of the α termination.

  19. Valence electron structure and properties of stabilized ZrO2

    Institute of Scientific and Technical Information of China (English)

    LI JinPing; HAN JieOai; MENG SongHe; ZHANG XingHong

    2008-01-01

    To reveal the properties of stabilizers in ZrO2 on nanoscopic levels,the valence elec-tron structures of four stable ZrO2 phases and c-ZrO2 were analyzed on the basis of the empirical electron theory of solids and molecules.The results showed that the hybridization levels of Zr atoms in c-ZrO2 doped with Ca and Mg dropped from B17 to B13,the hybridization levels of Zr atoms in c-ZrO2 doped with Y and Ce dropped from B17 to B15,and that the four stabilizing atoms all made the hybridization levels of O atoms drop from level 4 to level 2.The numbers of covalent electrons in the strongest covalent bond in the descending order are c-ZrO2>ZrCeO2>ZrYOZrMgO>ZrCaO.The bond energies of the strongest covalent bond and the melting points of the solid solutions in the descending order are ZrCeO2>c-ZrO2>ZrYO>ZrMgO>ZrCaO.The percent-ages of the total number of covalent electrons in the descending order arec-ZrO2>ZrYO> ZrCeO2>ZrMgO> ZrCaO.From the above analysis,it can be concluded that the stabilizing degrees of the four stabilizers in the descending order are CaO> MgO>Y2O3>CeO2.

  20. Valence, Implicated Actor, and Children's Acquiescence to False Suggestions.

    Science.gov (United States)

    Cleveland, Kyndra C; Quas, Jodi A; Lyon, Thomas D

    2016-01-01

    Although adverse effects of suggestive interviewing on children's accuracy are well documented, it remains unclear as to whether these effects vary depending on the valence of and the actor implicated in suggestions. In this study, 124 3-8-year-olds participated in a classroom activity and were later questioned about positive and negative false details. The interviewer provided positive reinforcement when children acquiesced to suggestions and negative feedback when they did not. Following reinforcement or feedback, young children were comparably suggestible for positive and negative details. With age, resistance to suggestions about negative details emerged first, followed by resistance to suggestions about positive details. Across age, more negative feedback was required to induce acquiescence to negative than positive false details. Finally, children were less willing to acquiesce when they (versus the confederate) were implicated. Findings highlight the interactive effects of valence and children's age on their eyewitness performance in suggestive contexts.

  1. Realistic estimate of valence transversity distributions from inclusive dihadron production

    CERN Document Server

    Radici, Marco; Bacchetta, Alessandro; Guagnelli, Marco

    2015-01-01

    We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. The e+e- data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

  2. Covert face recognition relies on affective valence in congenital prosopagnosia.

    Science.gov (United States)

    Bate, Sarah; Haslam, Catherine; Jansari, Ashok; Hodgson, Timothy L

    2009-06-01

    Dominant accounts of covert recognition in prosopagnosia assume subthreshold activation of face representations created prior to onset of the disorder. Yet, such accounts cannot explain covert recognition in congenital prosopagnosia, where the impairment is present from birth. Alternatively, covert recognition may rely on affective valence, yet no study has explored this possibility. The current study addressed this issue in 3 individuals with congenital prosopagnosia, using measures of the scanpath to indicate recognition. Participants were asked to memorize 30 faces paired with descriptions of aggressive, nice, or neutral behaviours. In a later recognition test, eye movements were monitored while participants discriminated studied from novel faces. Sampling was reduced for studied--nice compared to studied--aggressive faces, and performance for studied--neutral and novel faces fell between these two conditions. This pattern of findings suggests that (a) positive emotion can facilitate processing in prosopagnosia, and (b) covert recognition may rely on emotional valence rather than familiarity.

  3. Valence-band states of ion-bombarded polystyrene

    Energy Technology Data Exchange (ETDEWEB)

    Terrasi, A. (Istituto di Metodologie e Tecnologie per la Microelettronica, CNR, Corso Italia 57, 95129 Catania, Italy (IT)); Foti, G. (Dipartimento di Fisica, Universita di Catania, Corso Italia 57, 95129 Catania, (Italy)); Hwu, Y. (Synchrotron Radiation Center, University of Wisconsin-Madison, 3731 Schneider Drive, Stoughton, Wisconsin 53589-3097 (USA)); Margaritondo, G. (Ecole Polytechnique Federale de Lausanne, Department de Physique, PHB-Ecublens, CH 1015 Lausanne, (Switzerland))

    1991-08-01

    Ion-bombarded polystyrene with a 0.5-keV Ar{sup +} beam has been investigated by means of photoelectron spectroscopy performed with synchrotron radiation. After a dose of 10{sup 15} ions/cm{sup 2} the evolution of the valence band of the bombarded sample towards an amorphous carbonlike configuration is reported. From the analysis of valence-band spectra we estimated the out-diffusion of hydrogen and showed that its electronic states remain well identified and stable until the hydrogen presence is about 35% with respect to the pristine sample. Finally, comparison with mass spectroscopy measurements on deuterated polystyrene has been performed to determine hydrogen evolution during the ion irradiation.

  4. Realistic estimate of valence transversity from dihadron production

    CERN Document Server

    Radici, Marco

    2015-01-01

    We have updated our extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. The most recent COMPASS data for proton and deuteron targets, complemented by previous HERMES data on the proton, make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in $e^+ e^-$ annihilation. The $e^+ e^-$ data from BELLE have been reanalyzed to reach a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

  5. Configuration of the valence neutrons of 17B

    Institute of Scientific and Technical Information of China (English)

    WANG Meng; MAO Rui-Shi; ZHANG Hong-Bin; ZHAO Tie-Cheng; XU Zhi-Guo; WANG Yue; CHEN Ruo-Fu; HUANG Tian-Heng; GAO Hui; JIA Fei; FU Fen; HU Zheng-Guo; GAO Qi; HAN Jian-Long; ZHANG Xue-Heng; ZHENG Chuan; YU Yu-Hong; FAN Rui-Rui; LI Bo; GUO Zhong-Yan; XU Hu-Shan; SUN Zhi-Yu; WANG Jian-Song; XIAO Guo-Qing; ZHAN Wen-Long; ZHANG Xue-Ying; LI Chen

    2008-01-01

    The reaction cross section of 17B on 12C target at (43.7±2.4) MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (Rrms) was deduced to be (2.92±0.10) fm, while the Rrms of the core and the valence neutron distribution are 2.28 fm and 5.98 fm respectively. Assuming a "core plus 2n" structure in 17B, the mixed configuration of (2s1/2) and (1d5/2) of the valence neutrons is studied and the s-wave spectroscopic factor is found to be (80±21)%.

  6. Results from overlap valence quarks on a twisted mass sea

    CERN Document Server

    Garron, N

    2007-01-01

    We present results of lattice computations using overlap fermions on a twisted mass background. $N_f=2$ full QCD gauge configurations have been produced by the ETM Collaboration with very light pions (down to less than 300 MeV), with small lattice spacing ($a \\approx 0.09$ fm) and large volumes ($V/a^4=24^3\\times 48$). By profiting of the good chiral properties of the overlap operator for the valence quarks, it is also possible to have a precise (and unquenched) determination of those physical quantities where the chiral properties are crucial. In order to have unquenched results, we match the valence quark mass with the sea quark mass. We also perform computations with different quark masses in order to simulate (partially quenched) Strange and Charm quarks. A typical application is the computation of $B_K$, for which we present first results.

  7. Verbal pragmatics following unilateral stroke: emotional content and valence.

    Science.gov (United States)

    Borod, J C; Rorie, K D; Pick, L H; Bloom, R L; Andelman, F; Campbell, A L; Obler, L K; Tweedy, J R; Welkowitz, J; Sliwinski, M

    2000-01-01

    Verbal pragmatic aspects of discourse production were examined in 16 right brain-damaged (RBD), 16 left brain-damaged (LBD), and 16 normal control right-handed adults. The facilitation effect of emotional content, valence hypothesis, and relationship between pragmatics and emotion were evaluated. Participants produced monologues while recollecting emotional and nonemotional experiences. Transcribed monologues were rated for appropriateness on 6 pragmatic features: conciseness, lexical selection, quantity, relevancy, specificity, and topic maintenance. Overall, brain-damaged groups were rated as significantly less appropriate than normals. Consistent with the facilitation effect, emotional content enhanced pragmatic performance of LBD aphasic participants yet suppressed performance of RBD participants. Contrary to the valence hypothesis, RBD participants were more impaired for positive emotions and LBD participants for negative emotions. Pragmatic appropriateness was not strongly correlated with a measure of emotional intensity.

  8. Structure and dynamics of La(III) in aqueous solution An ab initio QM/MM MD approach

    Science.gov (United States)

    Hofer, Thomas S.; Scharnagl, Harald; Randolf, Bernhard R.; Rode, Bernd M.

    2006-08-01

    Ab initio QM/MM MD simulations have allowed to clarify some of the ambiguities arising from various studies on the hydrated La(III) ion. Both nine- and ten-coordinated hydrates co-exist and interchange in a dissociative process on the nano- or even subnanosecond scale, and thus much faster than any other trivalent main group or transition metal ions. The weak ion-ligand bond (53 N/m) supplies a reasonable explanation for it. The simulation results for La(III) are also compared to those for the isoelectronic ions Cs(I) and Ba(II) obtained by the same ab initio MD procedure, leading to conclusions on the influence of central ion charge on structural and dynamic properties of hydrate complexes.

  9. Ab-initio vibrational properties of transition metal chalcopyrite alloys determined as high-efficiency intermediate-band photovoltaic materials

    Energy Technology Data Exchange (ETDEWEB)

    Palacios, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain); Instituto de Catalisis y Petroleoquimica, CSIC. Marie Curie 2, Cantoblanco, 28049 Madrid (Spain)], E-mail: pablop@etsit.upm.es; Aguilera, I.; Wahnon, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain)

    2008-08-30

    In this work, we present frozen phonon and linear response ab-initio research into the vibrational properties of the CuGaS{sub 2} chalcopyrite and transition metal substituted (CuGaS{sub 2})M alloys. These systems are potential candidates for developing a novel solar-cell material with enhanced optoelectronic properties based in the implementation of the intermediate-band concept. We have previously carried out ab-initio calculations of the electronic properties of these kinds of chalcopyrite metal alloys showing a narrow transition metal band isolated in the semiconductor band gap. The substitutes used in the present work are the 3d metal elements, Titanium and Chromium. For the theoretical calculations we use standard density functional theory at local density and generalized gradient approximation levels. We found that the optical phonon branches of the transition metal chalcopyrite, are very sensitive to the specific bonding geometry and small changes in the transition metal environment.

  10. Theoretical study of ionic liquids based on the cholinium cation. Ab initio simulations of their condensed phases

    Science.gov (United States)

    Campetella, Marco; Bodo, Enrico; Montagna, Maria; De Santis, Serena; Gontrani, Lorenzo

    2016-03-01

    We have explored by means of ab initio molecular dynamics the homologue series of 11 different ionic liquids based on the combination of the cholinium cation with deprotonated amino acid anions. We present a structural analysis of the liquid states of these compounds as revealed by accurate ab initio computations of the forces. We highlight the persistent structural motifs that see the ionic couple as the basic building block of the liquid whereby a strong hydrogen bonding network substantially determines the short range structural behavior of the bulk state. Other minor docking features of the interaction network are also discovered and described. Special cases along the series such as Cysteine and Phenylalanine are discussed in the view of their peculiar properties due to zwitterion formation and additional long-range structural organization.

  11. Continuum-limit scaling of overlap fermions as valence quarks

    Energy Technology Data Exchange (ETDEWEB)

    Cichy, Krzysztof [Adam Mickiewicz Univ., Poznan (Poland). Faculty of Physics; Herdoiza, Gregorio; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

    2009-10-15

    We present the results of a mixed action approach, employing dynamical twisted mass fermions in the sea sector and overlap valence fermions, with the aim of testing the continuum limit scaling behaviour of physical quantities, taking the pion decay constant as an example. To render the computations practical, we impose for this purpose a fixed finite volume with lattice size L{approx}1.3 fm. We also briefly review the techniques we have used to deal with overlap fermions. (orig.)

  12. Valence holes observed in nanodiamonds dispersed in water.

    Science.gov (United States)

    Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F

    2015-02-21

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp(2)-hybridized carbon disappear, and holes in the valence band are observed.

  13. Valence parity renders z(*)-type ions chemically distinct.

    Science.gov (United States)

    Hubler, Shane L; Jue, April; Keith, Jason; McAlister, Graeme C; Craciun, Gheorghe; Coon, Joshua J

    2008-05-21

    Here we report that the odd electron z (*) -type ions formed by the electron-based peptide dissociation methods (electron capture or transfer, ECD or ETD) have distinctive chemical compositions from other common product ion types. Specifically, b-, c-, and y-type ions have an odd number of atoms with an odd valence (e.g., N and H), while z (*)-type ions contain an even number of atoms with an odd valence. This tenet, referred to as the valence parity rule, mandates that no c-type ion shall have the same chemical composition, and by extension mass, as a z (*) -type ion. By experiment we demonstrate that nearly half of all observed c- and z (*) -type product ions resulting from 226 ETD product ion spectra can be assigned to a single, correct, chemical composition and ion type by simple inspection of the m/ z peaks. The assignments provide (1) a platform to directly determine amino acid composition, (2) an input for database search algorithms, or (3) a basis for de novo sequence analysis.

  14. Sketching the pion's valence-quark generalised parton distribution

    Directory of Open Access Journals (Sweden)

    C. Mezrag

    2015-02-01

    Full Text Available In order to learn effectively from measurements of generalised parton distributions (GPDs, it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL truncation of QCD's Dyson–Schwinger equations and exemplified via the pion's valence dressed-quark GPD, Hπv(x,ξ,t. Our analysis focuses primarily on ξ=0, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting Hπv(x,ξ=±1,t with the pion's valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for Hπv(x,0,t, expressed as the Radon transform of a single amplitude. Therewith we obtain results for Hπv(x,0,t and the associated impact-parameter dependent distribution, qπv(x,|b→⊥|, which provide a qualitatively sound picture of the pion's dressed-quark structure at a hadronic scale. We evolve the distributions to a scale ζ=2 GeV, so as to facilitate comparisons in future with results from experiment or other nonperturbative methods.

  15. The valence and spectral properties of rare-earth clusters

    CERN Document Server

    Peters, L; Litsarev, M S; Katsnelson, A Delin M I; Kirilyuk, A; Johansson, B; Sanyal, B; Eriksson, O

    2016-01-01

    The rare-earths are known to have intriguing changes of the valence, depending on chemical surrounding or geometry. Here we make predictions from theory that combines density functional theory with atomic multiplet-theory, on the transition of valence when transferring from the atomic divalent limit to the trivalent bulk, passing through different sized clusters, of selected rare-earths. We predict that Tm clusters show an abrupt change from pure divalent to pure trivalent at a size of 6 atoms, while Sm and Tb clusters are respectively pure divalent and trivalent up to 8 atoms. Larger Sm clusters are argued to likely make a transition to a mixed valent, or trivalent, configuration. The valence of all rare-earth clusters, as a function of size, is predicted from interpolation of our calculated results. We argue that the here predicted behavior is best analyzed by spectroscopic measurements, and provide theoretical spectra, based on dynamical mean field theory, in the Hubbard-I approximation, to ease experiment...

  16. Basic features of the pion valence-quark distribution function

    Directory of Open Access Journals (Sweden)

    Lei Chang

    2014-10-01

    Full Text Available The impulse-approximation expression used hitherto to define the pion's valence-quark distribution function is flawed because it omits contributions from the gluons which bind quarks into the pion. A corrected leading-order expression produces the model-independent result that quarks dressed via the rainbow–ladder truncation, or any practical analogue, carry all the pion's light-front momentum at a characteristic hadronic scale. Corrections to the leading contribution may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we use an algebraic model to express the principal impact of both classes of corrections. This enables a realistic comparison with experiment that allows us to highlight the basic features of the pion's measurable valence-quark distribution, qπ(x; namely, at a characteristic hadronic scale, qπ(x∼(1−x2 for x≳0.85; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum.

  17. Characterization of the valence and conduction bands in Si nanocrystals

    Science.gov (United States)

    van Buuren, T.; Terminello, L.; Chase, L.; Callcott, T.; Grush, M.

    1998-03-01

    Silicon nanocrystals with a mean diameter between 1 and 4 nm were produced by thermal evaporation of Si in Ar buffer gas and deposited on a substrate. The size-distribution and diameter of the clusters were characterized by atomic force microscopy. The valence and conduction band edges of the Si nanocrystals were measured in-situ using soft x-ray emission (SXE) and absorption (XAS) spectroscopies. The valence band of the smallest Si nanocrystals is shifted by much as 0.7 eV relative to bulk Si. Significant changes in the shape of the spectra are also observed between the Si nanocrytals and bulk Si. We interpret the shift and changes in the spectra of the valence band as resulting from an altered electronic band structure in the confined Si structures. A smaller but proportional shift of the conduction band to higher energy is also observed in the XAS spectra of the silicon nanostructures. We compare the experimentally measured bandgap to recent electronic structure calculations and find, that the experimentally measured bandgap is smaller than that predicted by theory. Work supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract W-7405-ENG-48.

  18. Sketching the pion's valence-quark generalised parton distribution

    CERN Document Server

    Mezrag, C; Moutarde, H; Roberts, C D; Rodriguez-Quintero, J; Sabatie, F; Schmidt, S M

    2014-01-01

    In order to learn effectively from measurements of generalised parton distributions (GPDs), it is desirable to compute them using a framework that can potentially connect empirical information with basic features of the Standard Model. We sketch an approach to such computations, based upon a rainbow-ladder (RL) truncation of QCD's Dyson-Schwinger equations and exemplified via the pion's valence dressed-quark GPD, $H_\\pi^{\\rm v}(x,\\xi,t)$. Our analysis focuses primarily on $\\xi=0$, although we also capitalise on the symmetry-preserving nature of the RL truncation by connecting $H_\\pi^{\\rm v}(x,\\xi=\\pm 1,t)$ with the pion's valence-quark parton distribution amplitude. We explain that the impulse-approximation used hitherto to define the pion's valence dressed-quark GPD is generally invalid owing to omission of contributions from the gluons which bind dressed-quarks into the pion. A simple correction enables us to identify a practicable improvement to the approximation for $H_\\pi^{\\rm v}(x,0,t)$, expressed as th...

  19. Optimizing electronic structure and quantum transport at the graphene-Si(111) interface: an ab initio density-functional study.

    Science.gov (United States)

    Tayran, Ceren; Zhu, Zhen; Baldoni, Matteo; Selli, Daniele; Seifert, Gotthard; Tománek, David

    2013-04-26

    We use ab initio density-functional calculations to determine the interaction of a graphene monolayer with the Si(111) surface. We find that graphene forms strong bonds to the bare substrate and accommodates the 12% lattice mismatch by forming a wavy structure consisting of free-standing conductive ridges that are connected by ribbon-shaped regions of graphene, which bond covalently to the substrate. We perform quantum transport calculations for different geometries to study changes in the transport properties of graphene introduced by the wavy structure and bonding to the Si substrate. Our results suggest that wavy graphene combines high mobility along the ridges with efficient carrier injection into Si in the contact regions.

  20. All Electron ab initio Investigations of the Three Lowest Lying Electronic States of the RuC Molecule

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, K. A.

    2000-01-01

    The three lowest-lying electronic states of RuC, (1)Sigma(+), (3)Delta, and (1)Delta, have been investigated by performing all-electron ab initio multi-configuration self-consistent-field (CASSCF) and multi-reference configuration interaction (MRCI) calculations including relativistic corrections....... The electronic ground state is derived as (1)Sigma(+) with the spectroscopic constants r(e) = 1.616 Angstrom and omega(e) = 1085 cm(-1). The lowest-lying excited state, (3)Delta, has r(e) = 1.632 Angstrom, omega(e) = 1063 cm(-1), and T-e = 912 cm(-1). These results are consistent with recent spectroscopic values....... The chemical bonds in all three lowest-lying states are triple bonds composed of one sigma and two pi bonds. (C) 2000 Elsevier Science B.V. All rights reserved....

  1. Ab initio studies on the structure of and atomic interactions in cellulose III(I) crystals.

    Science.gov (United States)

    Ishikawa, Tetsuya; Hayakawa, Daichi; Miyamoto, Hitomi; Ozawa, Motoyasu; Ozawa, Tomonaga; Ueda, Kazuyoshi

    2015-11-19

    The crystal structure of cellulose III(I)was analyzed using first-principles density functional theory (DFT). The geometry was optimized using variable-cell relaxation, as implemented in Quantum ESPRESSO. The Perdew-Burke-Ernzerhof (PBE) functional with a correction term for long-range van der Waals interactions (PBE-D) reproduced the experimental structure well. By using the optimized crystal structure, the interactions existed among the cellulose chains in the crystal were precisely investigated using the NBO analysis. The results showed that the weak bonding nature of CH/O and the hydrogen bonding occur among glucose molecules in the optimized crystal structure. To investigate the strength of interaction, dimeric and trimeric glucose units were extracted from the crystal, and analyzed using MP2 ab initio counterpoise methods with BSSE correction. The results estimated the strength of the interactions. That is, the packed chains along with a-axis interacts with weak bonding nature of CH/O and dispersion interactions by -7.50 kcal/mol, and two hydrogen bonds of O2HO2…O6 and O6HO6…O2 connect the neighboring packed chains with -11.9 kcal/mol. Moreover, FMO4 calculation was also applied to the optimized crystal structure to estimate the strength of the interactions. These methods can well estimate the interactions existed in the crystal structure of cellulose III(I).

  2. X-ray absorption of liquid water studied by advanced ab initio methods

    Science.gov (United States)

    Sun, Zhaoru; Wang, Jianping; Kang, Wei; Car, Roberto; Wu, Xifan

    Oxygen K-edge X-ray absorption spectra (XAS) provide a sensitive local probe of the H-bond structure of liquid water. Based on the static COHSEX approach, we computed the XAS spectra of liquid water from molecular structures generated by ab initio molecular dynamics (AIMD) simulations using a van der Waals (vdW) inclusive hybrid functional (PBE0) that gives ambient water structure in quantitative agreement with experiment [JCP 141, 084502 (2014)]. We find that good agreement between experimental and theoretical XAS requires both improved molecular modeling and excitation treatment. In our simulation the over-structured H-bond network resulting from GGA-AIMD is systematically reduced as the directional H-bond strength is lowered by the mitigated self-interaction error in PBE0 and the increased population of interstitial water molecules promoted by vdW interactions. The better H-bond structure in turn gives improved XAS spectra. Moreover, we find that the orbitals obtained from the self-consistent diagonalization of the self-energy are crucial in obtaining spectra that compare well with experiment. Doe SciDAC: DE-SC0008626 and DE-SC0008726.

  3. Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

    Energy Technology Data Exchange (ETDEWEB)

    Cieplicka-Oryńczak, N. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Fornal, B.; Szpak, B. [Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Leoni, S.; Bottoni, S. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Bazzacco, D. [Dipartimento di Fisica e Astronomia dell’Università, I-35131 Padova (Italy); INFN Sezione di Padova, I-35131 Padova (Italy); Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T. [Institute Laue-Langevin, 6, rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Bocchi, G. [Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); France, G. de [GANIL, Bd. Becquerel, BP 55027, 14076 CAEN Cedex 05 (France); Simpson, G. [LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, F-38026 Grenoble Cedex (France); Ur, C. [INFN Sezione di Padova, Via F. Marzolo 8, I-35131 Padova (Italy); Urban, W. [Faculty of Physics, University of Warsaw, ul. Hoża 69, 02-681, Warszawa (Poland)

    2015-10-15

    The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility of testing the calculations involving the core excitations.

  4. On pleasure and thrill: the interplay between arousal and valence during visual word recognition.

    Science.gov (United States)

    Recio, Guillermo; Conrad, Markus; Hansen, Laura B; Jacobs, Arthur M

    2014-07-01

    We investigated the interplay between arousal and valence in the early processing of affective words. Event-related potentials (ERPs) were recorded while participants read words organized in an orthogonal design with the factors valence (positive, negative, neutral) and arousal (low, medium, high) in a lexical decision task. We observed faster reaction times for words of positive valence and for those of high arousal. Data from ERPs showed increased early posterior negativity (EPN) suggesting improved visual processing of these conditions. Valence effects appeared for medium and low arousal and were absent for high arousal. Arousal effects were obtained for neutral and negative words but were absent for positive words. These results suggest independent contributions of arousal and valence at early attentional stages of processing. Arousal effects preceded valence effects in the ERP data suggesting that arousal serves as an early alert system preparing a subsequent evaluation in terms of valence. Copyright © 2014 Elsevier Inc. All rights reserved.

  5. Identification of the Molecule-Metal Bonding Geometries of Molecular Nanowires

    CERN Document Server

    Demir, Firuz

    2011-01-01

    Molecular nanowires in which a single molecule bonds chemically to two metal electrodes and forms a stable electrically conducting bridge between them have been studied intensively for more than a decade. However the experimental determination of the bonding geometry between the molecule and electrodes has remained elusive. Here we demonstrate by means of ab initio calculations that inelastic tunneling spectroscopy (IETS) can determine these geometries. We identify the bonding geometries at the gold-sulfur interfaces of propanedithiolate molecules bridging gold electrodes that give rise to the specific IETS signatures that were observed in recent experiments.

  6. Ab initio Computations of the Electronic, Mechanical, and Thermal Properties of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2

    Science.gov (United States)

    Lawson, John W.; Bauschlicher, Charles W.; Daw, Murray

    2011-01-01

    Refractory materials such as metallic borides, often considered as ultra high temperature ceramics (UHTC), are characterized by high melting point, high hardness, and good chemical inertness. These materials have many applications which require high temperature materials that can operate with no or limited oxidation. Ab initio, first principles methods are the most accurate modeling approaches available and represent a parameter free description of the material based on the quantum mechanical equations. Using these methods, many of the intrinsic properties of these material can be obtained. We performed ab initio calculations based on density functional theory for the UHTC materials ZrB2 and HfB2. Computational results are presented for structural information (lattice constants, bond lengths, etc), electronic structure (bonding motifs, densities of states, band structure, etc), thermal quantities (phonon spectra, phonon densities of states, specific heat), as well as information about point defects such as vacancy and antisite formation energies.

  7. Mechanism for Si–Si Bond Rupture in Single Molecule Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Haixing; Kim, Nathaniel T.; Su, Timothy A.; Steigerwald, Michael L.; Nuckolls, Colin; Darancet, Pierre; Leighton, James L.; Venkataraman, Latha

    2016-12-14

    The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si–Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si–Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si–Si bond is ruptured using an applied voltage. We investigate this voltage induced Si–Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation of molecular vibrational modes by tunneling electrons leads to homolytic Si–Si bond rupture.

  8. [V16O38(CN)]9–: a soluble mixed-valence redox-active building block with strong antiferromagnetic coupling.

    Science.gov (United States)

    Keene, Tony D; D'Alessandro, Deanna M; Krämer, Karl W; Price, Jason R; Price, David J; Decurtins, Silvio; Kepert, Cameron J

    2012-09-03

    A new discrete [V(16)O(38)(CN)](9-) cluster, which displays the hitherto unknown 8- charge on the cluster shell and is the first to encapsulate the cyanide anion, has been synthesized and characterized by IR and UV/vis/near-IR spectroscopy, electrochemistry, and magnetic susceptibility measurements. Bond valence sum calculations conducted on the basis of the crystal structure analysis of K(9)[V(16)O(38)(CN)]·13H(2)O confirm that this new member of the polyoxovanadate series is a mixed-valence complex. The intervalence charge transfer bands arising from intrametal interactions reveal that a localized (class II) assignment is appropriate for the cluster; however, a small degree of electronic delocalization is present. Interesting possibilities exist for the incorporation of this unit into higher dimensionality framework structures, where the redox, optical, and magnetic properties can be exploited and tuned.

  9. Two-dimensional Penning ionization electron spectroscopy of open-shell metallocenes: outer valence ionic states of vanadocene and nickelocene.

    Science.gov (United States)

    Kishimoto, Naoki; Kimura, Miku; Ohno, Koichi

    2013-04-11

    In order to investigate outer valence ionic states of open-shell metallocenes, we have applied two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy (2D-PIES) upon collision with metastable He*(2(3)S) excited atoms as well as a high level ab initio molecular orbital calculation (the partial third-order quasiparticle theory of the electron propagator (P3)) to ionization from neutral ground states of vanadocene ((4)A2g) and nickelocene ((3)A2g). Assignments of observed Penning ionization electron/He I ultraviolet photoelectron spectra were consistent with the P3 calculation results for ionization of α and β spin electrons except for electron correlation bands observed by PIES. Negative collision energy dependence of partial Penning ionization cross-sections (CEDPICS) indicate attractive interaction with He*(2(3)S) around the molecule. Results by model potential calculation utilizing Li(2(2)S) instead of He*(2(3)S) for interaction between He*(2(3)S) and open-shell metallocenes do not explain the strong negative CEDPICS of the bands observed in PIES.

  10. Valence electron energy-loss spectroscopy study of ZrSiO{sub 4} and ZrO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Nan, E-mail: nan.jiang@asu.edu; Spence, John C.H.

    2013-11-15

    ZrSiO{sub 4} (zircon) and m-ZrO{sub 2} (zirconia) are fundamental and industrially important materials. This work reports the detailed valence electron energy-loss spectroscopy (VEELS) studies of these compounds. The dielectric response functions, as well as single-electron interband transition spectra, are derived from VEELS data for both ZrSiO{sub 4} and m-ZrO{sub 2}, in the range 5–50 eV using the Kramers–Kronig analysis method. Our interpretation of the interband transitions is given with the aid of ab initio calculations of density of states. The bandgap energies for both materials are also measured using VEELS. The surface and bulk plasmons are identified: the surface plasmon peaks locate at around 12 eV, and two bulk plasmon peaks are ∼15–16 eV and ∼25–27 eV, respectively. Although similarities in the VEELS exist between ZrSiO{sub 4} and m-ZrO{sub 2}, two major differences are also noticed and explained in terms of composition and structure differences.

  11. Ab initio study of the low-lying electronic states of the CaO molecule

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Hossain; Brites, Vincent; Quere, Frederic Le [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France); Leonard, Celine, E-mail: celine.leonard@univ-paris-est.fr [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France)

    2011-07-28

    Graphical abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1{Pi}}, b{sup 3}{Sigma}{sup +} and A{sup 1}{Sigma}{sup +}, and the corresponding dipole moment functions have been determined using internally contracted multi-reference configuration interaction approaches. The spectroscopic constants associated with these electronic states are compared to experimental values. The corresponding electronic wavefunctions have also been analyzed using the dipole moment functions. Display Omitted Highlights: {yields} The five lowest electronic states of Cao have been determined ab initio at a high level of accuracy. {yields} Large active space, core-valence correlation and configuration interaction are required. {yields} The multi-configurational nature of the electronic ground state is confirmed as well as its monovalent and divalent ionic nature using dipole moment analysis. {yields} These interacting potentials will serve for future obtention of spin-rovibronic levels. - Abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1}{Pi}, b{sup 3}{Sigma}{sup +} and A{sup 1

  12. The T2 phase in the Nb-Si-B system studied by ab initio calculations and synchrotron X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Joubert, J.-M., E-mail: jean-marc.joubert@icmpe.cnrs.fr [Chimie Metallurgique des Terres Rares, Institut de Chimie et des Materiaux Paris-Est, CNRS, Universite Paris-Est, UMR 7182, 2-8 rue Henri Dunant, F-94320 Thiais, France. (France); Colinet, C. [Science et Ingenierie des Materiaux et Procedes, Grenoble INP, UJF, CNRS, 38402 Saint Martin d' Heres Cedex (France); Rodrigues, G. [Laboratorio de Materiais e Metalurgia, Instituto de Engenharia Mecanica, Universidade Federal de Itajuba, Av. BPS 1303, 37500-903 Itajuba-MG (Brazil); Mestrado Profissional em Materiais, Centro Universitario de Volta Redonda, Av. Paulo Erlei Alves Abrantes 1325, 27240-560 Volta Redonda-RJ (Brazil); Suzuki, P.A.; Nunes, C.A. [Departamento de Engenharia de Materiais, Escola de Engenharia de Lorena, Universidade de Sao Paulo, Caixa Posta 116, 12600-970 Lorena-SP (Brazil); Coelho, G.C. [Mestrado Profissional em Materiais, Centro Universitario de Volta Redonda, Av. Paulo Erlei Alves Abrantes 1325, 27240-560 Volta Redonda-RJ (Brazil); Departamento de Engenharia de Materiais, Escola de Engenharia de Lorena, Universidade de Sao Paulo, Caixa Posta 116, 12600-970 Lorena-SP (Brazil); Tedenac, J.-C. [Institut de Chimie Moleculaire et des Materiaux I.C.G., UMR-CNRS 5253, Universite Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5 (France)

    2012-06-15

    The solid solution based on Nb{sub 5}Si{sub 3} (Cr{sub 5}B{sub 3} structure type, D8{sub l}, tI32, I4/mcm, No140, a=6.5767 A, c=11.8967 A) in the Nb-Si-B system was studied from the structural and thermodynamic point of view both experimentally and by ab initio calculations. Rietveld refinement of powder X-ray synchrotron data allowed to determine the boron to silicon substitution mechanism and the structural parameters. Ab initio calculations of different ordered compounds and selected disordered alloys allowed to obtain in addition to the enthalpy of formation of the solution, substitution mechanism and structural parameters which are in excellent agreement with the experimental data. The stability of the phase is discussed. - Graphial abstract: Valence-charge electron localization function in the z=0 plane of the D8{sub l} structure for the ordered compound Nb{sub 5}SiB{sub 2}. Highlights: Black-Right-Pointing-Pointer Coupling between ab initio data and experimental results from synchrotron powder diffraction. Black-Right-Pointing-Pointer Excellent agreement between the two techniques for the site occupancies and internal coordinates. Black-Right-Pointing-Pointer Explanation of the phase stability up to Nb{sub 5}SiB{sub 2}.

  13. Alkali metal mediated C-C bond coupling reaction.

    Science.gov (United States)

    Tachikawa, Hiroto

    2015-02-14

    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2](-) was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results.

  14. Ferromagnetic bond of Li10 cluster: An alternative approach in terms of effective ferromagnetic sites

    Science.gov (United States)

    Donoso, Roberto; Rössler, Jaime; Llano-Gil, Sandra; Fuentealba, Patricio; Cárdenas, Carlos

    2016-09-01

    In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li10 and Li8 clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

  15. Vibrations and hydrogen bonding in porphycene.

    Science.gov (United States)

    Gawinkowski, Sylwester; Walewski, Łukasz; Vdovin, Alexander; Slenczka, Alkwin; Rols, Stephane; Johnson, Mark R; Lesyng, Bogdan; Waluk, Jacek

    2012-04-28

    Combined use of IR, Raman, neutron scattering and fluorescence measurements for porphycene isolated in helium nanodroplets, supersonic jet and cryogenic matrices, as well as for solid and liquid solutions, resulted in the assignments of almost all of 108 fundamental vibrations. The puzzling feature of porphycene is the apparent lack of the N-H stretching band in the IR spectrum, predicted to be the strongest of all bands by standard harmonic calculations. Theoretical modeling of the IR spectra, based on ab initio molecular dynamics simulations, reveals that the N-H stretching mode should appear as an extremely broad band in the 2250-3000 cm(-1) region. Coupling of the N-H stretching vibration to other modes is discussed in the context of multidimensional character of intramolecular double hydrogen transfer in porphycene. The analysis can be generalized to other strongly hydrogen-bonded systems. This journal is © the Owner Societies 2012

  16. The site occupation and valence of Mn ions in the crystal lattice of Sr{sub 4}Al{sub 14}O{sub 25} and its deep red emission for high color-rendering white light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Lei, E-mail: shanggan2009@qq.com [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Xue, Shaochan; Chen, Xiuling [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Bahader, Ali [Department of Chemistry, Hazara University, Mansehra 21300 (Pakistan); Deng, Xiaorong; Zhao, Erlong; Jiang, Yang [School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009 (China); Chen, Shifu, E-mail: chshifu@chnu.edu.cn [Department of Chemistry, Huaibei Normal University, Huaibei 235000 (China); Chan, Ting-Shan [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, ROC (China); Zhao, Zhi; Zhang, Wenhua [National Synchrotron Radiation Laboratory, University of Science and Technology, Hefei, Anhui 230026 (China)

    2014-12-15

    Highlights: • Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were identified using XANES and EPR. • Red luminescence was attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. • The Mn{sup 3+} incorporated in the center of AlO{sub 4} tetrahedron was non-luminescent. • The bond-valence theory was used to analyze the effective valences of cations. • A white LED device with CRI up to Ra 93.23 was packaged by using the red phosphor. - Abstract: The synthesis and component of red phosphor, Sr{sub 4}Al{sub 14}O{sub 25}: Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr{sup 2+} and Al{sup 3+} in Sr{sub 4}Al{sub 14}O{sub 25}. As a result, the strong covalence of Al{sup 3+} in the AlO{sub 4} tetrahedron other than in the AlO{sub 6} octahedron is disclosed. The deep red emission is attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. The mechanism of energy transfer is mainly through dipole–dipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability.

  17. Operator evolution for ab initio nuclear theory

    CERN Document Server

    Schuster, Micah D; Johnson, Calvin W; Jurgenson, Eric D; Navratil, Petr

    2014-01-01

    The past two decades have seen a revolution in ab initio calculations of nuclear properties. One key element has been the development of a rigorous effective interaction theory, applying unitary transformations to soften the nuclear Hamiltonian and hence accelerate the convergence as a function of the model space size. For consistency, however, one ought to apply the same transformation to other operators when calculating transitions and mean values from the eigenstates of the renormalized Hamiltonian. Working in a translationally-invariant harmonic oscillator basis for the two- and three-nucleon systems, we evolve the Hamiltonian, square-radius and total dipole strength operators by the similarity renormalization group (SRG). The inclusion of up to three-body matrix elements in the 4He nucleus all but completely restores the invariance of the expectation values under the transformation. We also consider a Gaussian operator with adjustable range and find at short ranges an increased contribution from such ind...

  18. Discovering chemistry with an ab initio nanoreactor

    Science.gov (United States)

    Martinez, Todd

    Traditional approaches for modeling chemical reaction networks such as those involved in combustion have focused on identifying individual reactions and using theoretical approaches to explore the underlying mechanisms. Recent advances involving graphical processing units (GPUs), commodity products developed for the videogaming industry, have made it possible to consider a distinct approach wherein one attempts to discover chemical reactions and mechanisms. We provide a brief summary of these developments and then discuss the concept behind the ``ab initio nanoreactor'' which explores the space of possible chemical reactions and molecular species for a given stoichiometry. The nanoreactor concept is exemplified with an example to the Urey-Miller reaction network which has been previously advanced as a potential model for prebiotic chemistry. We briefly discuss some of the future directions envisioned for the development of this nanoreactor concept.

  19. Ab initio alpha-alpha scattering

    CERN Document Server

    Elhatisari, Serdar; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G

    2015-01-01

    Processes involving alpha particles and alpha-like nuclei comprise a major part of stellar nucleosynthesis and hypothesized mechanisms for thermonuclear supernovae. In an effort towards understanding alpha processes from first principles, we describe in this letter the first ab initio calculation of alpha-alpha scattering. We use lattice effective field theory to describe the low-energy interactions of nucleons and apply a technique called the adiabatic projection method to reduce the eight-body system to an effective two-cluster system. We find good agreement between lattice results and experimental phase shifts for S-wave and D-wave scattering. The computational scaling with particle number suggests that alpha processes involving heavier nuclei are also within reach in the near future.

  20. An ab initio study of hydroxylated graphane

    Science.gov (United States)

    Buonocore, Francesco; Capasso, Andrea; Lisi, Nicola

    2017-09-01

    Graphene-based derivatives with covalent functionalization and well-defined stoichiometry are highly desirable in view of their application as functional surfaces. Here, we have evaluated by ab initio calculations the energy of formation and the phase diagram of hydroxylated graphane structures, i.e., fully functionalized graphene derivatives coordinated with -H and -OH groups. We compared these structures to different hydrogenated and non-hydrogenated graphene oxide derivatives, with high level of epoxide and hydroxyl groups functionalization. Based on our calculations, stable phases of hydroxylated graphane with low and high contents of hydrogen are demonstrated for high oxygen and hydrogen partial pressure, respectively. Stable phases of graphene oxide with a mixed carbon hybridization are also found. Notably, the synthesis of hydroxylated graphane has been recently reported in the literature.

  1. Giant magnetoresistance An ab-initio description

    CERN Document Server

    Binder, J

    2000-01-01

    A new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened KORRINGA-KOHNROSTOKER method. Scattering at impurity atoms in the multilayers is described by means of a GREEN's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the BOLTZMANN equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the BOLTZMANN equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the...

  2. Discovering chemistry with an ab initio nanoreactor

    Science.gov (United States)

    Wang, Lee-Ping; Titov, Alexey; McGibbon, Robert; Liu, Fang; Pande, Vijay S.; Martínez, Todd J.

    2014-12-01

    Chemical understanding is driven by the experimental discovery of new compounds and reactivity, and is supported by theory and computation that provide detailed physical insight. Although theoretical and computational studies have generally focused on specific processes or mechanistic hypotheses, recent methodological and computational advances harken the advent of their principal role in discovery. Here we report the development and application of the ab initio nanoreactor—a highly accelerated first-principles molecular dynamics simulation of chemical reactions that discovers new molecules and mechanisms without preordained reaction coordinates or elementary steps. Using the nanoreactor, we show new pathways for glycine synthesis from primitive compounds proposed to exist on the early Earth, which provide new insight into the classic Urey-Miller experiment. These results highlight the emergence of theoretical and computational chemistry as a tool for discovery, in addition to its traditional role of interpreting experimental findings.

  3. Valence-quark distribution functions in the kaon and pion

    Science.gov (United States)

    Chen, Chen; Chang, Lei; Roberts, Craig D.; Wan, Shaolong; Zong, Hong-Shi

    2016-04-01

    We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed quarks carry all the meson's momentum at a characteristic hadronic scale and vanish as (1 -x )2 when Bjorken-x →1 . Comparing such distributions within the pion and kaon, it is apparent that the size of S U (3 ) -flavor symmetry breaking in meson parton distribution functions is modulated by the flavor dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulas may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two thirds of the pion's light-front momentum is carried by valence dressed quarks at a characteristic hadronic scale; this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of u -quark distributions that is in agreement with the single existing data set, and predicts a u -quark distribution within the pion that agrees with a modern reappraisal of π N Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.

  4. Valence-quark distribution functions in the kaon and pion

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Chen; Chang, Lei; Roberts, Craig D.; Wan, Shaolong; Zong, Hong-Shi

    2016-04-18

    We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed quarks carry all the meson’s momentum at a characteristic hadronic scale and vanish as ( 1 - x ) 2 when Bjorken- x → 1 . Comparing such distributions within the pion and kaon, it is apparent that the size of S U ( 3 ) -flavor symmetry breaking in meson parton distribution functions is modulated by the flavor dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulas may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two thirds of the pion’s light-front momentum is carried by valence dressed quarks at a characteristic hadronic scale; this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of u -quark distributions that is in agreement with the single existing data set, and predicts a u -quark distribution within the pion that agrees with a modern reappraisal of π N Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.

  5. Crystal structures of two mixed-valence copper cyanide complexes with N-methyl-ethylenedi-amine.

    Science.gov (United States)

    Corfield, Peter W R; Sabatino, Alexander

    2017-02-01

    The crystal structures of two mixed-valence copper cyanide compounds involving N-methyl-ethylenedi-amine (meen), are described. In compound (I), poly[bis(μ3-cyanido-κ3C:C:N)tris(μ2-cyanido-κ2C:N)bis(N-methylethane-1,2-di-amine-κ2N,N')tricopper(I)copper(II)], [Cu4(CN)5(C3H10N2)2] or Cu4(CN)5meen2, cyanide groups link Cu(I) atoms into a three-dimensional network containing open channels parallel to the b axis. In the network, two tetra-hedrally bound Cu(I) atoms are bonded by the C atoms of two end-on bridging CN groups to form Cu2(CN)6 moieties with the Cu atoms in close contact at 2.560 (1) Å. Other trigonally bound Cu(I) atoms link these units together to form the network. The Cu(II) atoms, coordinated by two meen units, are covalently linked to the network via a cyanide bridge, and project into the open network channels. In the mol-ecular compound (II), [(N-methylethylenediamine-κ(2)N,N')copper(II)]-μ(2)-cyanido-κ(2)C:N-[bis(cyanido-κC)copper(I)] monohydrate, [Cu2(CN)3(C3H10N2)2]·H2O or Cu2(CN)3meen2·H2O, a CN group connects a Cu(II) atom coordinated by two meen groups with a trigonal-planar Cu(I) atom coordinated by CN groups. The mol-ecules are linked into centrosymmetric dimers via hydrogen bonds to two water mol-ecules. In both compounds, the bridging cyanide between the Cu(II) and Cu(I) atoms has the N atom bonded to Cu(II) and the C atom bonded to Cu(I), and the Cu(II) atoms are in a square-pyramidal coordination.

  6. Electron Momentum Spectroscopy of Ethanethiol Complete Valence Shell

    Institute of Scientific and Technical Information of China (English)

    Xin-xia Xue; Mi Yan; Fang Wu; Xu Shan; Ke-zun Xu; Xiang-jun Chen

    2008-01-01

    The binding energy spectra and electron momentum distributions for the complete valence orbitals of ethanethiol were measured for the first time by binary (e, 2e) electron momentum spectroscopy employing non-coplanar symmetric kinematics at an impact energy of 1200 eV plus binding energy. The experimental results are generally consistent with the theoretical calculations using density functional theory and Hartree-Fock methods with various basis sets. A possible satellite line at 17.8 eV in binding energy spectrum was observed and studied by electron momentum spectroscopy.

  7. Valence-band photoemission intensities in thorium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Ellis, W.P.; Boring, A.M.; Cox, L.E.; Cowan, R.D.; Arko, A.J. (Los Alamos National Lab., NM (USA)); Allen, J.W. (Michigan Univ., Ann Arbor, MI (USA). Dept. of Physics); Pate, B.B.; Lindau, I. (Stanford Univ., CA (USA). Synchrotron Radiation Lab.)

    1989-11-01

    Resonant photoemission spectra of the O 2p-derived valence band of insulating ThO{sub 2} are compared to linear muffin-tin orbital (LMTO) density-of-state (DOS) and XPS intensity calculations. At Th 5d core-level threshold energies (85 {le} hv {le} 120 eV), resonance is greatest at the bottom of the O 2p band where calculated p/d hybrid states are greatest; p/f hybrid content is weak by comparison. We conclude that the dominant hybridization is between O 2p states and Th 6d. (author).

  8. Towards ab initio self-energy embedding theory in quantum chemistry

    CERN Document Server

    Lan, Tran Nguyen; Zgid, Dominika

    2015-01-01

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function (GF2) method is used to describe the non-local correlations, while the full configuration interaction (FCI) method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to $n-$electron valence state second-order perturbation theory (NEVPT2) with the same active...

  9. An ab initio study of the polytypism in InP

    Science.gov (United States)

    Dacal, Luis C. O.; Cantarero, A.

    2016-09-01

    The existence of polytypism in semiconductor nanostructures gives rise to the appearance of stacking faults which many times can be treated as quantum wells. In some cases, despite of a careful growth, the polytypism can be hardly avoided. In this work, we perform an ab initio study of zincblende stacking faults in a wurtzite InP system, using the supercell approach and taking the limit of low density of narrow stacking faults regions. Our results confirm the type II band alignment between the phases, producing a reliable qualitative description of the band gap evolution along the growth axis. These results show an spacial asymmetry in the zincblende quantum wells, that is expected due to the fact that the wurtzite stacking sequence (ABAB) is part of the zincblende one (ABCABC), but with an unexpected asymmetry between the valence and the conduction bands. We also present results for the complex dielectric function, clearly showing the influence of the stacking on the homostructure values and surprisingly proving that the correspondent bulk results can be used to reproduce the polytypism even in the limit we considered.

  10. Morse-Smale Analysis of Ion Diffusion in Ab Initio Battery Materials Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Gyulassy, Attila [Univ. of Utah, Salt Lake City, UT (United States); Knoll, Aaron [Univ. of Utah, Salt Lake City, UT (United States); Lau, Kah Chun [Argonne National Lab. (ANL), Argonne, IL (United States); Wang, Bei [Univ. of Utah, Salt Lake City, UT (United States); Bremer, Peer-Timo [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Papka, Michael [Argonne National Lab. (ANL), Argonne, IL (United States); Curtiss, Larry A [Argonne National Lab. (ANL), Argonne, IL (United States); Pascucci, Valerio [Univ. of Utah, Salt Lake City, UT (United States)

    2017-06-03

    Ab initio molecular dynamics (AIMD) simulations are increasingly useful in modeling, optimizing and synthesizing materials in energy sciences. In solving Schrödinger’s equation, they generate the electronic structure of the simulated atoms as a scalar field. However, methods for analyzing these volume data are not yet common in molecular visualization. The Morse-Smale complex is a proven, versatile tool for topological analysis of scalar fields. In this paper, we apply the discrete Morse-Smale complex to analysis of first-principles battery materials simulations. We consider a carbon nanosphere structure used in battery materials research, and employ Morse-Smale decomposition to determine the possible lithium ion diffusion paths within that structure. Our approach is novel in that it uses the wavefunction itself as opposed distance fields, and that we analyze the 1-skeleton of the Morse-Smale complex to reconstruct our diffusion paths. Furthermore, it is the first application where specific motifs in the graph structure of the complete 1-skeleton define features, namely carbon rings with specific valence. We compare our analysis of DFT data with that of a distance field approximation, and discuss implications on larger classical molecular dynamics simulations.

  11. Communication: Towards ab initio self-energy embedding theory in quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Tran Nguyen, E-mail: latran@umich.edu [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Kananenka, Alexei A.; Zgid, Dominika [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2015-12-28

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green’s function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.

  12. Ab initio study of charge, spin and orbital ordering in manganites

    CERN Document Server

    Tyer, R

    2001-01-01

    The subject of this thesis was the calculation of the electronic structure for the manganites LaMnO sub 3 and CaMnO sub 3. The implementation of the Self-Interaction Corrected Local Spin Density (SIC-LSD) formalism within the Tight Binding Linear Muffin-Tin Orbital method in conjunction with the Atomic Sphere Approximation was used for these calculations. The SIC-LSD total energy functional has been used to investigate the spin ordering and valency of CaMnO sub 3 and LaMnO sub 3. In order to assess the role of the structural distortion in LaMnO sub 3 , these calculations were performed for an idealised cubic structure as well as for the observed distorted orthorhombic structure. Orbital rotations of the localised (SIC corrected) states were implemented. These orbital rotations were then used to perform the first ab-initio investigation of orbital ordering in LaMnO sub 3. For the experimentally observed A-type antiferromagnetic ordering, the correct orbital structure of alternating manganese d sub 3 sub x sub ...

  13. Communication: Towards ab initio self-energy embedding theory in quantum chemistry.

    Science.gov (United States)

    Lan, Tran Nguyen; Kananenka, Alexei A; Zgid, Dominika

    2015-12-28

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.

  14. Ab-initio study of germanium di-interstitial using a hybrid functional (HSE)

    Science.gov (United States)

    Igumbor, E.; Ouma, C. N. M.; Webb, G.; Meyer, W. E.

    2016-01-01

    In this work, we present ab-initio calculation results of Ge di-interstitials (I2(Ge)) in the framework of the density functional theory (DFT) using the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional. The formation energy, transition levels and minimum energy configurations were obtained for I2(Ge) -2, -1, 0, +1 and +2 charge states. The calculated formation energies show that for all charge states of I2(Ge), the double tetrahedral (T) configuration formed the most stable defect with a binding energy of 1.24 eV in the neutral state. We found the (+2/+1) charge state transition level for the T lying below the conduction band minimum and (+2/+1) for the split[110]-tetrahedral configuration lying deep at 0.41 eV above the valence band maximum. The di-interstitials in Ge exhibited the properties of both shallow and deep donor levels at (+2/+1) within the band gap and depending on the configurations. I2(Ge) gave rise to negative-U, with effective-U values of -0.61 and -1.6 eV in different configurations. We have compared our results with calculations of di-interstitials in silicon and available experimental data.

  15. Band offset of the ZnO/Cu2O heterojunction from ab initio calculations

    Science.gov (United States)

    Zemzemi, M.; Alaya, S.

    2013-12-01

    The ZnO/Cu2O system has known a recent revival of interest in solar cells for its potential use as a heterojunction able to highly perform under visible light. In this work, we are interested on the characterization of the interface through nanoscale modelization based on ab initio (Density Functional Theory (DFT), Local Density Approximation (LDA), Generalized Gradient Approximation (GGA-PBE), and Pseudopotential (PP)). This work aims to build a supercell containing a heterojunction ZnO/Cu2O and study the structural properties and the discontinuity of the valence band (band offset) from a semiconductor to another. We built a zinc oxide in the wurtzite structure along the [0 0 0 1] on which we placed the copper oxide in the hexagonal structure (CdI2-type). We choose the method of Van de Walle and Martin to calculate the energy offset. This approach fits well with the DFT. Our calculations of the band offset gave us a value that corresponds to other experimental and theoretical values.

  16. Ab initio theory of exchange interactions and the Curie temperature of bulk Gd

    CERN Document Server

    Turek, I; Bihlmayer, G; Bluegel, S

    2003-01-01

    An ab initio approach to the magnetic properties of bulk hexagonal Gd is developed that is based on the local spin-density approximation with the 4f electrons treated as localized core electrons. The effective one-electron problem is solved using the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation with the valence basis consisting of s-, p-and d-type orbitals. The approach leads to a correct description of the ground-state properties like the stability of the ferromagnetic structure, the magnetic moment and the equilibrium lattice constant. Application of a real-space Green-function formalism yields the exchange pair interactions between distant neighbours that are inevitable for quantitative studies of magnetic excitations. The distance dependence and anisotropy of the exchange pair interactions are presented and the Curie temperature in the mean-field approximation is evaluated. The obtained value of 334 K is in much better agreement with the experimental value of 293 K tha...

  17. Ab‐initio study of germanium di-interstitial using a hybrid functional (HSE)

    Energy Technology Data Exchange (ETDEWEB)

    Igumbor, E., E-mail: elgumuk@gmail.com [Department of Physics, University of Pretoria, Pretoria 0002 (South Africa); Department of Mathematics and Physical Sciences, Samuel Adegboyega University, Km 1 Ogwa/Ehor Rd, Ogwa, Edo State (Nigeria); Ouma, C.N.M.; Webb, G. [Department of Physics, University of Pretoria, Pretoria 0002 (South Africa); Meyer, W.E., E-mail: wmeyer@up.ac.za [Department of Physics, University of Pretoria, Pretoria 0002 (South Africa)

    2016-01-01

    In this work, we present ab‐initio calculation results of Ge di-interstitials (I{sub 2(Ge)}) in the framework of the density functional theory (DFT) using the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional. The formation energy, transition levels and minimum energy configurations were obtained for I{sub 2(Ge)} −2, −1, 0, +1 and +2 charge states. The calculated formation energies show that for all charge states of I{sub 2(Ge)}, the double tetrahedral (T) configuration formed the most stable defect with a binding energy of 1.24 eV in the neutral state. We found the (+2/+1) charge state transition level for the T lying below the conduction band minimum and (+2/+1) for the split[110]-tetrahedral configuration lying deep at 0.41 eV above the valence band maximum. The di-interstitials in Ge exhibited the properties of both shallow and deep donor levels at (+2/+1) within the band gap and depending on the configurations. I{sub 2(Ge)} gave rise to negative-U, with effective-U values of −0.61 and −1.6 eV in different configurations. We have compared our results with calculations of di-interstitials in silicon and available experimental data.

  18. Ab initio ro-vibronic spectroscopy of SiCCl (X{sup ~2}Π)

    Energy Technology Data Exchange (ETDEWEB)

    Brites, Vincent [Université d’Evry Val d’Essonne, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, LAMBE CNRS UMR 8587, Boulevard F. Mitterrand, 91025 Evry Cedex (France); Mitrushchenkov, Alexander O.; Léonard, Céline, E-mail: celine.leonard@u-pem.fr [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Peterson, Kirk A. [Department of Chemistry, Washington State University, Pullman, Washington 99164 (United States)

    2014-07-21

    The full dimensional potential energy surfaces of the {sup 2}A{sup ′} and {sup 2}A{sup ′′} electronic components of X{sup ~2}Π SiCCl have been computed using the explicitly correlated coupled cluster method, UCCSD(T)-F12b, combined with a composite approach taking into account basis set incompleteness, core-valence correlation, scalar relativity, and higher order excitations. The spin-orbit and dipole moment surfaces have also been computed ab initio. The ro-vibronic energy levels and absorption spectrum at 5 K have been determined from variational calculations. The influence of each correction on the fundamental frequencies is discussed. An assignment is proposed for bands observed in the LIF experiment of Smith et al. [J. Chem. Phys. 117, 6446 (2002)]. The overall agreement between the experimental and calculated ro-vibronic levels is better than 7 cm{sup −1} which is comparable with the 10–20 cm{sup −1} resolution of the emission spectrum.

  19. A comparison of approaches to estimate the resonance energy

    NARCIS (Netherlands)

    Zielinski, Marcin; Havenith, Remco W. A.; Jenneskens, Leonardus W.; van Lenthe, Joop H.

    2010-01-01

    We discuss Ab Initio approaches to calculate the energy lowering (stabilisation) due to aromaticity. We compare the valence bond method and the block-localised wave function approaches to calculate the resonance energy. We conclude that the valence bond approach employs a Pauling-Wheland resonance e

  20. A comparison of approaches to estimate the resonance energy

    NARCIS (Netherlands)

    Zielinski, M.L.; Havenith, R.W.A.; Jenneskens, L.W.; van Lenthe, J.H.

    2010-01-01

    We discuss Ab Initio approaches to calculate the energy lowering (stabilisation) due to aromaticity. We compare the valence bond method and the block-localised wave function approaches to calculate the resonance energy. We conclude that the valence bond approach employs a Pauling–Wheland resonance e

  1. The effect of substituents on triply bonded boron[triple bond, length as m-dash]antimony molecules: a theoretical approach.

    Science.gov (United States)

    Lu, Jia-Syun; Yang, Ming-Chung; Su, Ming-Der

    2017-03-15

    Three (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B3LYP/LANL2DZ+dp) levels of theory are used to study the effect of substituents on the potential energy surfaces of RB[triple bond, length as m-dash]SbR (R = F, OH, H, CH3, SiH3, SiMe(SitBu3)2, SiiPrDis2 and NHC). The theoretical results demonstrate that the triply bonded RB[triple bond, length as m-dash]SbR molecules favor a bent geometry: that is, ∠R-B-Sb ≈ 180° and ∠B-Sb-R ≈ 120°. Regardless of the type of substituents that are attached to the RB[triple bond, length as m-dash]SbR compounds, theoretical evidence strongly indicates that their B[triple bond, length as m-dash]Sb triple bonds have a donor-acceptor nature and are proven to be very weak. Two valence bond models clarify the bonding characters of the B[triple bond, length as m-dash]Sb triple bond. For RB[triple bond, length as m-dash]SbR molecules that feature small substituents, the triple bond is represented as . For RB[triple bond, length as m-dash]SbR molecules that feature large substituents, the triple bond is represented as . Most importantly, this theoretical study predicts that only bulkier substituents significantly stabilize the triply bonded RB[triple bond, length as m-dash]SbR molecules, from the kinetic viewpoint.

  2. Obtaining detailed structural information about supramolecular systems on surfaces by combining high-resolution force microscopy with ab initio calculations.

    Science.gov (United States)

    Kawai, Shigeki; Sadeghi, Ali; Xu, Feng; Feng, Xu; Peng, Lifen; Lifen, Peng; Pawlak, Rémy; Glatzel, Thilo; Willand, Alexander; Orita, Akihiro; Otera, Junzo; Goedecker, Stefan; Meyer, Ernst

    2013-10-22

    State-of-the art experimental techniques such as scanning tunneling microscopy have great difficulties in extracting detailed structural information about molecules adsorbed on surfaces. By combining atomic force microscopy and Kelvin probe force microscopy with ab initio calculations, we demonstrate that we can obtain a wealth of detailed structural information about the molecule itself and its environment. Studying an FFPB molecule on a gold surface, we are able to determine its exact location on the surface, the nature of its bonding properties with neighboring molecules that lead to the growth of one-dimensional strips, and the internal torsions and bendings of the molecule.

  3. ELECTRONIC AND CHEMICAL PROPERTIES OF PD IN BIMETALLIC SYSTEMS: HOW MUCH DO WE KNOW ABOUT HETERONUCLEAR METAL-METAL BONDING?

    Energy Technology Data Exchange (ETDEWEB)

    RODRIGUEZ,J.A.

    2001-09-27

    The experimental and theoretical studies described above illustrate the complex nature of the heteronuclear metal-metal bond. In many cases, bimetallic bonding induces a significant redistribution of charge around the bonded metals. This redistribution of charge is usually linked to the strength of the bimetallic bond, affects the position of the core and valence levels of the metals, and can determine the chemical reactivity of the system under study. New concepts are emerging [22,23,34,36] and eventually the coupling of experiment and theory can be useful for designing more efficient bimetallic catalysts [98,106,107].

  4. Molecular determinants for drug-receptor interactions. Part 2. An ab initio molecular orbital and dipole moment study of the novel nootropic agent piracetam (2-oxopyrrolidin-1-ylacetamide)

    Science.gov (United States)

    Lumbroso, H.; Liégeois, C.; Pappalardo, G. C.; Grassi, A.

    From the ab initio molecular energies of the possible conformers and from a classical dipole moment analysis of 2-oxopyrrolidin-l-ylacetamide (μ = 4.02 D in dioxan at 30.0°C), the preferred conformation in solution of this novel nootropic agent has been determined. The exocyclic N-CH 2 bond is rotated in one sense by 90° and the exocyclic CH 2-C bond rotated in the same sense by 120° from the "planar" ( OO)- cis conformation. The structures of the two enantiomers in solution differ from that of the crystalline molecule.

  5. Bonding with Your Baby

    Science.gov (United States)

    ... in infant massage in your area. Breastfeeding and bottle-feeding are both natural times for bonding. Infants respond ... activities include: participating together in labor and delivery feeding ( breast or bottle ); sometimes dad forms a special bond with baby ...

  6. Redundant internal coordinates, compliance constants and non-bonded interactions - some new insights

    Indian Academy of Sciences (India)

    Moumita Majumder; Sadasivam Manogaran

    2013-01-01

    A long standing problem in normal mode analysis is identifying the right internal coordinates given only the cartesian coordinates, the masses of the atoms and the cartesian force constants without using any other additional chemical information. A possible solution is suggested here as drawing the normal modes obtained from the mass weighted cartesian force constant matrix and identifying the correct bonds and angles from the normal mode pictures. If chosen properly, the internal coordinates will have minimum mixing in the normal mode representation. This can in principle lead to an automation algorithm. A complete basis of internal coordinates is defined as the minimum number of valence internal coordinates that describe all the normal modes as completely as possible. It was shown in the literature that the relaxed force constants could be used as a measure of bond order in all atom-atom distance coordinates. Some of the bonded and non-bonded atom pairs can have similar values of the relaxed force constants and hence to use the relaxed force constant as a measure of bond order we need to separate the bonded pairs from the non-bonded ones. This needs extra chemical information of which pairs are bonded. The new definition of complete basis of non-redundant valence internal coordinates helps to identify the bonded pairs effectively without extra information. The hydrogen bonded water clusters (H2O), n = 2-6, methane dimer and methane-water complex are used as examples to verify that the relaxed force constants of bonded pairs are indeed a measure of bond order.

  7. Valence Topological Charge-Transfer Indices for Dipole Moments: Percutaneous Enhancers

    Directory of Open Access Journals (Sweden)

    Francisco Torrens

    2004-12-01

    Full Text Available Valence topological charge-transfer (CT indices are applied to the calculationof dipole moments. The algebraic and vector semisum CT indices are defined. Thecombination of CT indices allows the estimation of the dipole moments. The model isgeneralized for molecules with heteroatoms. The ability of the indices for the descriptionof the molecular charge distribution is established by comparing them with the dipolemoments of homologous series of percutaneous enhancers (phenyl alcohols and4-alkylanilines. Linear and quadratic correlation models are obtained. CT indicesimprove the multivariable quadratic regression equations for the dipole moment. Thevariance decreases 97% (4-alkylanilines. No superposition of the corresponding Gk–Jkand GkV–JkV pairs is observed in the fits, which diminishes the risk of co-linearity. Theinclusion of the heteroatom in the π-electron system is beneficial for the description ofthe dipole moment, owing to either the role of the additional p orbitals provided by theheteroatom or the role of steric factors in the π-electron conjugation. Inclusion of aconjugated double bond in the alkyl chain lends to more rigid structures with dipolemoment variations lower than1%.

  8. Nonideal anion displacement, band gap variation, and valence band splitting in Cu-In-Se compounds

    Energy Technology Data Exchange (ETDEWEB)

    Reena Philip, Rachel [Solid State Physics Laboratory, Department of Physics, Cochin University of Science and Technology, Kochi-682022 Kerala (India)]. E-mail: reenatara@cusat.ac.in; Pradeep, B. [Solid State Physics Laboratory, Department of Physics, Cochin University of Science and Technology, Kochi-682022 Kerala (India)

    2005-01-24

    Polycrystalline thin films of ternary chalcopyrite CuInSe{sub 2} and defect compounds CuIn{sub 3}Se{sub 5} and CuIn{sub 5}Se{sub 8} are prepared in vacuum by three-source coevaporation method. Structural and optical characterizations of the films are done using X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), and optical absorbance spectra measurements. With variation in the composition of CuInSe{sub 2}, a change over from p-type to n-type conductivity is observed (as noted by the hot probe method). The deformation parameters and the anion displacements are calculated from the X-ray diffraction data, and the cation-anion bond lengths are deduced. The dependence of band gap variation on nonideal anion displacement in the ternary compounds and the effect of Se-p-Cu-d repulsion on band gap are studied. The threefold optical structure observed in the fundamental absorption region of the absorption spectra is analysed to extract the valence band splitting parameters. Hopfields quasi-cubic model adapted for chalcopyrites with tetragonal deformation is used to determine the crystal field splittings and spin orbit splittings, and the linear hybridization model is used to calculate the percentage of d-orbital and p-orbital contribution to hybridization in the compounds under consideration.

  9. Crystal structure of a mixed-valence μ-oxide Sn12 cluster

    Directory of Open Access Journals (Sweden)

    Marina M. Kireenko

    2014-11-01

    Full Text Available The mixed-valence μ-oxide Sn12 cluster, decacarbonyltetra-μ4-oxido-hexa-μ3-oxido-tetrakis[μ-2,2′-(pyridine-2,6-diylbis(1,1-diphenylethanolato]decatin(IIditin(IVdimolybdenum(O(2 Mo—Sn toluene heptasolvate, [Mo2Sn12(C33H27NO24O10(CO10]·7C7H8, has a crystallographically imposed inversion centre. The asymmetric unit also contains three and a half toluene solvent molecules, one of which is disordered about a centre of symmetry. The complex molecule comprises six distinct Sn atom species with four different coordination numbers, namely 3, 4, 5, and 6. The SnII atoms forming the central Sn10O10 core adopt distorted trigonal–pyramidal, square-pyramidal and octahedral coordination geometries provided by the μ-oxide atoms and by the O- and N-donor atoms of two pyridinediethanolate ligands. The terminal SnIV atoms have distorted trigonal–bipyramidal coordination geometries, with a μ4-oxide atom and the N atom of a pyridinediethanolate ligand occupying the axial positions, and the Mo atom of a Mo(CO5 group and the alkoxy O atoms of a ligand forming the equatorial plane. In the crystal, weak intra- and intermolecular C—H...O hydrogen bonds are observed.

  10. Effect of Oxidation Degree on Valence Change and Distribution of Octahedral Fe Element in Biotite

    Directory of Open Access Journals (Sweden)

    Li Ziqian

    2017-01-01

    Full Text Available In this paper, the valence change and distribution of iron elements in octahedral vacancies of biotite were studied in the oxidation process. The biotite and saturated barium nitrate solution were mixed in dilute hydrochloric acid under hydrothermal reaction conditions, the solid after reaction was used as the test sample. Firstly, the remainder potassium and iron content were measured by atomic absorption spectrometry(AAS. Secondly, the state of iron along with oxidation degree increased was analyzed, in addition, the phase composition and the change of layer spacing in samples was detected by X-ray diffraction(XRD. Thirdly, The variation mode of Si-O bond were characterized by Fourier transform infrared spectroscopy(FT-IR.This research was adopted hydrogen ions in diluted hydrochloric acid and nitrate ions in barium nitrate to provide oxidation environment for reaction, and the oxidation degree was controlled by adjusted the amount of hydrogen ion introduced. We found out that the amount of hydrogen ion is positively correlated with oxidation degree in biotite, and the deeper oxidation degree in biotite, the lower electronegativity of singer layer. Potassium and iron element would be release out of micaceous structure during the biotite oxidation. The higher the oxidation degree is, the greater the releasing happen. The charge density combining Fe oxidation and releasing firstly increased then decreased with the oxidation degree turned greater. During the oxidation, the Si-O vibrated would change from parallel layer vibration model to vertical vibration model.

  11. Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, J., E-mail: Julian.Fischer@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Music, D. [RWTH Aachen University, Materials Chemistry, Kopernikusstrasse 10, 52074 Aachen (Germany); Bergfeldt, T.; Ziebert, C.; Ulrich, S.; Seifert, H.J. [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2014-12-01

    This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn{sub 2}O{sub 4}-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn{sub 2}O{sub 4}-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn{sub 2}O{sub 4}.

  12. Bond percolation in films

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1988-04-01

    Bond percolation in films with simple cubic structure is considered. It is assumed that the probability of a bond being present between nearest-neighbor sites depends on the distances to surfaces. Based on the relation between the Potts model and the bond percolation model, and using the mean-field approximation, the phase diagram and profiles of the percolation probability have been obtained.

  13. Acrylic mechanical bond tests

    Energy Technology Data Exchange (ETDEWEB)

    Wouters, J.M.; Doe, P.J.

    1991-02-01

    The tensile strength of bonded acrylic is tested as a function of bond joint thickness. 0.125 in. thick bond joints were found to posses the maximum strength while the acceptable range of joints varied from 0.063 in. to almost 0.25 in. Such joints are used in the Sudbury Neutrino Observatory.

  14. Processing negative valence of word pairs that include a positive word.

    Science.gov (United States)

    Itkes, Oksana; Mashal, Nira

    2016-09-01

    Previous research has suggested that cognitive performance is interrupted by negative relative to neutral or positive stimuli. We examined whether negative valence affects performance at the word or phrase level. Participants performed a semantic decision task on word pairs that included either a negative or a positive target word. In Experiment 1, the valence of the target word was congruent with the overall valence conveyed by the word pair (e.g., fat kid). As expected, response times were slower in the negative condition relative to the positive condition. Experiment 2 included target words that were incongruent with the overall valence of the word pair (e.g., fat salary). Response times were longer for word pairs whose overall valence was negative relative to positive, even though these word pairs included a positive word. Our findings support the Cognitive Primacy Hypothesis, according to which emotional valence is extracted after conceptual processing is complete.

  15. Expertise in video game playing is associated with reduced valence-concordant emotional expressivity.

    Science.gov (United States)

    Weinreich, André; Strobach, Tilo; Schubert, Torsten

    2015-01-01

    In carefully selected groups of video game playing (VGP) experts and nonexperts, we examined valence-concordant emotional expressivity. We measured electromyographic (EMG) activity over the corrugator supercilii muscle while participants viewed pleasant, neutral, and unpleasant pictures. Potential group differences concerning valence-concordant expressivity may arise from differences concerning the participants' emotional reactivity. To control for such differences, we concomitantly measured skin conductance response (SCR) and, in a separate affect misattribution procedure (AMP), valence transfer from the same set of stimuli. Importantly, we found attenuated valence-concordant EMG activity over the corrugator supercilii muscle in VGP experts compared to nonexperts, but no differences were evident concerning SCR or valence transfer in the AMP. The findings suggest that expertise in VGP is particularly associated with reduced valence-concordant emotional expressivity.

  16. Virtual Distance and Soundstage, and their Impacts on Experienced Emotional Valence

    DEFF Research Database (Denmark)

    Christensen, Justin

    2015-01-01

    Research from animal ethology and affective neuroscience suggest that a listener’s perceived distance from a signal source can alter their experienced emotional valence of the music. Furthermore, appraisal theories of emotion suggest that emotionally valenced responses will diverge according...... to the type of emotion presented. For these exploratory investigations, subjects listen to selected musical excerpts on speakers in combination with a tactile transducer attached to their chair. The listening sessions are recorded on EEG supported by subject feedback responses. My hypothesis is that musical...... stimuli should cause stronger valenced responses in the nearfield than at a distance. Thus, music experienced as being negatively valenced at a distance should be more negatively valenced in nearfield, and music that is experienced as having a positive valence at a distance should be more positively...

  17. Ab-Initio-Based Approach to Study Complete Metalloproteins: Divide and Conquer Geometry Optimization of Nitric-Oxide Reductase

    Science.gov (United States)

    Yue, Yutao; Chachiyo, Teepanis; Rodriguez, Jorge H.

    2007-03-01

    The direct application of ab-initio methods (Hartree-Fock or density functional theory) to study complete biomolecules has been impossible due to the huge computational cost of fully quantum mechanical calculations. As an initial step towards overcoming this problem, we implemented an ab-initio-based method to predict geometric structures of large metalloproteins using the principle of ``divide and conquer.'' The method has been applied to small test systems showing satisfactory agreement with all-atom ab initio calculations. We have successfully applied the divide and conquer approach to partially optimize the geometry of a ligand-enzyme system, namely NO binding to nitric-oxide reductases (NOR, P450nor). NOR is a metalloenzyme that catalyzes the reduction of NO to N2O. To compare our results with all atom calculations we studied a biochemically relevant subsystem (375 atoms) of the ligand-enzyme complex. The deviation between the divide and conquer geometry and the all atom partial geometry optimization is minor, on order of 10-1 å for bond lengths. The computational cost of the method is moderately expensive making its application to large (bio) molecules plausible. Supported by NSF CAREER Award CHE-0349189 (JHR).

  18. Valence holes observed in nanodiamonds dispersed in water

    Science.gov (United States)

    Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F.

    2015-02-01

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed.Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed. Electronic supplementary information (ESI) available: Experimental methods, details on XAS/XES normalization and background correction procedures. See DOI: 10.1039/c4nr06639a

  19. Relative Contribution of Odour Intensity and Valence to Moral Decisions.

    Science.gov (United States)

    Cecchetto, Cinzia; Rumiati, Raffaella Ida; Parma, Valentina

    2017-01-01

    Meta-analytic evidence showed that the chemical senses affect moral decisions. However, how odours impact on morality is currently unclear. Through a set of three studies, we assess whether and how odour intensity biases moral choices (Study 1a), its psychophysiological responses (Study 1b), as well as the behavioural and psychophysiological effects of odour valence on moral choices (Study 2). Study 1a suggests that the presence of an odour plays a role in shaping moral choice. Study 1b reveals that of two iso-pleasant versions of the same neutral odour, only the one presented sub-threshold (vs. supra-threshold) favours deontological moral choices, those based on the principle of not harming others even when such harm provides benefits. As expected, this odour intensity effect is tracked by skin conductance responses, whereas no difference in cardiac activity - proxy for the valence dimension - is revealed. Study 2 suggests that the same neutral odour presented sub-threshold increases deontological choices even when compared to iso-intense ambiguous odour, perceived as pleasant or unpleasant by half of the participants, respectively. Skin conductance responses, as expected, track odour pleasantness, but cardiac activity fails to do so. Results are discussed in the context of mechanisms alternative to disgust induction underlying moral choices.

  20. Ligand-hole localization in oxides with unusual valence Fe.

    Science.gov (United States)

    Chen, Wei-Tin; Saito, Takashi; Hayashi, Naoaki; Takano, Mikio; Shimakawa, Yuichi

    2012-01-01

    Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe⁴⁺ → 2Fe³⁺ + 2Fe⁵⁺) in CaCu₃Fe₄O₁₂ and intersite charge transfer (3Cu²⁺ + 4Fe³·⁷⁵⁺ → 3Cu³⁺ + 4Fe³⁺) in LaCu₃Fe₄O₁₂. Here we report the synthesis of solid solutions of CaCu₃Fe₄O₁₂ and LaCu₃Fe₄O₁₂ and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu₃Fe₄O₁₂ is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu₃Fe₄O₁₂ is regarded as a Mott transition of the ligand holes.