A survey of recent developments in ab initio valence bond theory

Hiberty, Philippe C.; Shaik, Sason

doi:10.1002/jcc.20478

Cited by 84 publications

(72 citation statements)

References 181 publications

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“…As such, only three structures, one covalent and two ionic, are involved in the VB calculation, shown in Scheme 2 b. As the highest VB level, [26] we selected here the breathing-orbital VB method (BOVB).…”

Section: Vb Methodologymentioning

confidence: 99%

“…In a second calculation we used bond-distorted orbitals (BDOs), [26,33] wherein the HAO on one inverted carbon atom is allowed to delocalized only to the second inverted atom, across the target CÀC bond. This last calculation is equivalent to the threestructure calculation (Scheme 2), to within 1-2 kcal mol À1 at the standard VBSCF computational level.…”

Section: The Role Of Electron Delocalization In Bondingmentioning

confidence: 99%

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An Excursion from Normal to Inverted CC Bonds Shows a Clear Demarcation between Covalent and Charge‐Shift CC Bonds

Shaik

Chen

et al. 2009

ChemPhysChem

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What is the nature of the C-C bond? Valence bond and electron density computations of 16 C-C bonds show two families of bonds that flesh out as a phase diagram. One family, involving ethane, cyclopropane and so forth, is typified by covalent C-C bonding wherein covalent spin-pairing accounts for most of the bond energy. The second family includes the inverted bridgehead bonds of small propellanes, where the bond is neither covalent nor ionic, but owes its existence to the resonance stabilization between the respective structures; hence a charge-shift (CS) bond. The dual family also emerges from calculated and experimental electron density properties. Covalent C-C bonds are characterized by negative Laplacians of the density, whereas CS-bonds display small or positive Laplacians. The positive Laplacian defines a region suffering from neighbouring repulsive interactions, which is precisely the case in the inverted bonding region. Such regions are rich in kinetic energy, and indeed the energy-density analysis reveals that CS-bonds are richer in kinetic energy than the covalent C-C bonds. The large covalent-ionic resonance energy is precisely the mechanism that lowers the kinetic energy in the bonding region and restores equilibrium bonding. Thus, different degrees of repulsive strain create two bonding families of the same chemical bond made from a single atomic constituent. It is further shown that the idea of repulsive strain is portable and can predict the properties of propellanes of various sizes and different wing substituents. Experimentally (M. Messerschmidt, S. Scheins, L. Bruberth, M. Patzel, G. Szeimies, C. Paulman, P. Luger, Angew. Chem. 2005, 117, 3993-3997; Angew. Chem. Int. Ed. 2005, 44, 3925-3928), the C-C bond families are beautifully represented in [1.1.1]propellane, where the inverted C-C is a CS-bond, while the wings are made from covalent C-C bonds. What other manifestations can we expect from CS-bonds? Answers from experiment have the potential of recharting the mental map of chemical bonding.

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Section: Vb Methodologymentioning

confidence: 99%

Section: The Role Of Electron Delocalization In Bondingmentioning

confidence: 99%

An Excursion from Normal to Inverted CC Bonds Shows a Clear Demarcation between Covalent and Charge‐Shift CC Bonds

Shaik

Chen

et al. 2009

ChemPhysChem

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“…There are several computational approaches for VB theory at the ab initio level [5,7]. In the VB self-consistent field (VBSCF) procedure [50], both the VB orbitals and structural coefficients are optimized simultaneously to minimize the total energy.…”

Section: The Vb Levelsmentioning

confidence: 99%

“…As well-known examples, spin-coupled (SC) theory [1,2] and generalized valence bond (GVB) theory [3,4] are able to provide the most possible compact wave functions taking care of most of the static correlation energy in a molecule. Moreover, other VB-type methods include also dynamic correlation in a simple and lucid way [5][6][7][8]. Usually, dynamic correlation is retrieved in the MO framework by means of complete active space self-consistent-field approach (CASSCF) followed by a perturbative treatment (CASPT2), while VB methods may include dynamic correlation without increasing the number of VB structures, e.g., by using the breathing orbital effect [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

The V state of ethylene: valence bond theory takes up the challenge

Zhang

Braı̈da

et al. 2014

Theor Chem Acc

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HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. Further improvement to 7.96/7.93 eV is achieved at the variational and diffusion Monte Carlo (MC) levels, respectively, VMC/DMC, using a Jastrow factor coupled with the same compact VB wave function. Furthermore, the measure of the spatial extension of the V state wave function, 19.14 a 0 2 , is in the range of accepted values obtained by large-scale state-of-the-art molecular orbitalbased methods. The r response to the fluctuations of the p electrons in the V state, known to be a crucial feature of the V state, is taken into account using the breathing orbital valence bond method, which allows the VB structures to have different sets of orbitals. Further valence bond calculations in a larger space of configurations, involving explicit participation of the r response, with 9 VB structures for the N state and 14 for the V state, confirm the results of the minimal structure set, yielding an N ? V transition energy of 7.97 eV and a spatial extension of 19.16 a 0 2 for the V state. Both types of valence bond calculations show that the V state of ethylene is not fully ionic as usually assumed, but involving also a symmetryadapted combination of VB structures each with asymmetric covalent p bonds. The latter VB structures have cumulated weights of 18-26 % and stabilize the V state by about 0.9 eV. It is further shown that these latter VB structures, rather than the commonly considered zwitterionic ones, are the ones responsible for the spatial extension of the V state, known to be ca. 50 % larger than the V state.Keywords Valence bond Á Quantum Monte Carlo Á V state of ethylene Á Breathing orbitals 1 Introduction

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“…Unlike HartreeFock (or molecular orbital, MO) theory, GVB theory has the advantage of being inherently multi-reference and therefore able to describe bond dissociation and formation. A subset of the GVB orbitals (n a ) are singly occupied, instead of doubly occupied, and the GVB wave function can be written as follows [18][19][20][21].…”

Section: Methodsmentioning

confidence: 99%

The nature of the SO bond of chlorinated sulfur–oxygen compounds

Lindquist

Dunning

2014

Theor Chem Acc

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Sulfur-oxygen chemistry encompasses a rich variety of chemical species and reactions. Sulfur-oxygen bonds can be quite short and strong, and historically, there has been disagreement as to the nature of the SO bond in sulfinyl groups. Early work invoked participation by the 3d orbitals of sulfur to explain the apparent double-bond character of sulfinyl bonds, but modern calculations have clearly established that sulfur 3d atomic orbitals do not participate as valence orbitals in hypervalent sulfur compounds. In prior work, we used generalized valence bond (GVB) theory to explain the features of the SO bond in the HSO/SOH structural isomers, and we extend that work here to the chlorinated analogs (ClSO/SOCl). We also use GVB theory to elucidate the nature of the bonding in Cl 2 SO and its higher energy structural isomer ClSOCl. We find that recoupled pair bonding, which we first introduced in our study of sulfur fluorides, is integral to describing the SO bond in all of these species. We also connect our analysis to the use of hyperconjugation to explain the backbonding in the p system in the sulfinyl halides.

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A survey of recent developments in ab initio valence bond theory

Cited by 84 publications

References 181 publications

An Excursion from Normal to Inverted CC Bonds Shows a Clear Demarcation between Covalent and Charge‐Shift CC Bonds

An Excursion from Normal to Inverted CC Bonds Shows a Clear Demarcation between Covalent and Charge‐Shift CC Bonds

The V state of ethylene: valence bond theory takes up the challenge

The nature of the SO bond of chlorinated sulfur–oxygen compounds

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