Identity Hydrogen Abstraction Reactions, X• + H−X‘ → X−H + X‘• (X = X‘ = CH3, SiH3, GeH3, SnH3, PbH3):  A Valence Bond Modeling

Shaik, Sason; Wu, Wei; Dong, Kunming; Song, Lingchun; Hiberty, Philippe C.

doi:10.1021/jp011251c

Cited by 65 publications

(83 citation statements)

References 48 publications

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“…[106][107][108] Moreover, owing to the use of strictly localized active orbitals, these methods are suitable for calculating clearly defined diabatic states that are required to retain the physical content of a given asymptotic state, at any point of a reaction coordinate, without collapsing to the ground state by virtue of uncontrolled orbital optimization. 25,109,110 The Valence Bond Self Consistent Field Method…”

Section: Pure Vb Methods That Use Localized Orbitalsmentioning

confidence: 99%

A survey of recent developments in ab initio valence bond theory

Hiberty

Shaik

2006

J Comput Chem

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Starting from the 1980s and onwards, Valence Bond theory has been enjoying renaissance that is characterized by the development of a growing number of ab initio methods, and by many applications to chemical reactivity and to the central paradigms of chemistry. Owing the increase of computational power of modern computers and to significant advances in the methodology, valence bond theory begins to offer a sound and attractive alternative to Molecular Orbital theory. This review aims at summarizing the most important developments of ab initio valence bond methods during the last two or three decades, and is primarily devoted to a description of what the various methods can actually achieve within their specific scopes and limitations. Key available softwares are surveyed.

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Section: Pure Vb Methods That Use Localized Orbitalsmentioning

confidence: 99%

A survey of recent developments in ab initio valence bond theory

Hiberty

Shaik

2006

J Comput Chem

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“…Structures 7 and 8 are excited states that can mix only into the TS but do not contribute to the reactants and products. [35] ¹ The VB state correlation diagram (VBSCD) method: The VBSCD [21] method uses VB theory to provide chemical insight into the barrier and other features of a chemical reaction. The diagram, shown in Figure 1, is composed of three curves: one is the adiabatic energy profile of the ground state involving all eight structures in Scheme 1, and the other two are the reactant and product curves, also called diabatic curves.…”

Section: Methodsmentioning

confidence: 99%

“…[35] In a nutshell, after construction of these three curves, the barrier can then be analyzed in terms of the diabatic quantities. These are the promotion gap, G, the height of the crossing point, DE c , given as a fraction of the gap, ¦G, and the resonance energy of the transition state, B, which results from avoided crossing and VB mixing.…”

Section: Methodsmentioning

confidence: 99%

“…These are the promotion gap, G, the height of the crossing point, DE c , given as a fraction of the gap, ¦G, and the resonance energy of the transition state, B, which results from avoided crossing and VB mixing. [21,35,39] While full variation is suitable for the adiabatic curve that obeys the variational theorem, this may not necessarily be the case for the diabatic curves. Except for their asymptotic points, the diabatic curves are not physical states, and therefore a straightforward variational procedure may result in a wrong description of the diabatic curve.…”

Section: Methodsmentioning

confidence: 99%

“…(8)]. [35,39] G % 0.75DE ST (8) This equation, the derivation of which was elaborated in previous treatments of the VBSCD, [35,39] is a good approximation to G. However, a precise estimate of G is given in Equation 7, as the average of the singlet-to-triplet excitation and the corresponding bond energy [Eq. (9)] where D is the bond energy of H 2.…”

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See 2 more Smart Citations

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

Song

Hiberty

et al. 2003

Chemistry A European J

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One of the landmark achievements of quantum chemistry, specifically of MO-based methods that include electron correlation, was the precise calculation of the barrier for the hydrogen-exchange reaction (B. Liu, J. Chem. Phys. 1973, 58, 1925; P. Siegbahn, B. Liu, J. Chem. Phys. 1978, 68, 2457). This paper reports an accurate calculation of this barrier by two recently developed VB methods that use only the eight classical VB structures. To our knowledge, the present work is the first accurate ab initio VB barrier that matches an experimental value. Along with the accurate barrier, the VB method provides accurate bond energies and diabatic quantities that enable the barrier height to be analyzed by the VB state correlation diagram approach, VBSCD (S. Shaik, A. Shurki, Angew. Chem. 1999, 111, 616; Angew. Chem. Int. Ed. Engl. 1999, 38, 586). This is a proof of principal that VB theory with appropriate account of dynamic electron correlation can achieve quantitative accuracy of reaction barriers, and still retain a compact and interpretable wave function. A sample of S(N)2 barriers and dihalogen bonding energies, which are close to CCSD(T) and G2(+) values, show that the H(3) problem is not an isolated case, and while it is premature to conclude that VB theory has come of age, the occurrence of this event is clearly within sight.

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VBCI : A Valence Bond Configuration Interaction Method that Includes Dynamic Correlation

Song

Zhang

et al. 1998

Encyclopedia of Computational Chemistry

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Valence bond configuration interaction (VBCI) is introduced in this paper. The method adds the dynamic correlation contribution by use of configuration interaction (CI) following a VBSCF calculation. The VBCI method allows various approaches with different structure selection procedures. VBCIS involves only single excitations, while VBCISD involves also doubles, and so on. VBCI(D, S) includes doubly excited structures for the active electron shell and singly excited structures for inactive pairs. Using perturbation theory, VBCIPT truncates less important excitations and estimates their contribution by an approximate perturbation theoretic formula. The methods were tested by calculating the bond energies of H 2 , LiH, HF, HCl, F 2 , and Cl 2 as well as the barriers of identity hydrogen abstraction reactions, X• + X′H → XH + X′• (X, X′ = CH 3 , SiH 3 , GeH 3 , SnH 3 , PbH 3 ). Test calculations show the VBCISD results match those of the MO‐based CCSD method. The computational results of VBCI(D, S) and VBCIPT match those of VBCISD with much less computational effort. As a demonstration of the potential of the VBCI method, we calculated the barrier of the hydrogen exchange reaction. The value of 10.0 kcal mol −1 of the VBCI barrier is in very good agreement with the most accurate barrier of MO–based methods.

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Identity Hydrogen Abstraction Reactions, X^• + H−X‘ → X−H + X‘^• (X = X‘ = CH₃, SiH₃, GeH₃, SnH₃, PbH₃): A Valence Bond Modeling

Cited by 65 publications

References 48 publications

A survey of recent developments in ab initio valence bond theory

A survey of recent developments in ab initio valence bond theory

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

VBCI : A Valence Bond Configuration Interaction Method that Includes Dynamic Correlation

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