Applications of spin-coupled valence bond theory

Cooper, David L.; Gerratt, Joseph; Raimondi, Mario

doi:10.1021/cr00005a014

Cited by 292 publications

(149 citation statements)

References 18 publications

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“…Besides, the slight nonequivalence of CASSCF and VBSCF calculations even when both span the same variational space [6] has also been pointed out. 1 The importance of structures 4a and 4b can be appreciated by performing a VB study in a smaller space, restricted to 2, 3a, and 3b. The results at the VBSCF and BOVB levels (referred to as VBSCF-3 and BOVB-3, respectively) show that removing 4a and 4b from the VB space causes a considerable increase in the transition energy relative to the reference VBSCF-5 and BOVB-5 levels, in both 6-31G* and cc-pVTZ basis sets, indicating that structures 4a and 4b stabilize the V state by some 0.7-0.9 eV.…”

Section: Vb Calculations In the (2 2) Spacementioning

confidence: 99%

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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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Section: Vb Calculations In the (2 2) Spacementioning

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].…”

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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“…Because of immense debt which chemistry owes to the classical model of molecule as composed of directionally oriented and well localized chemical bonds, it is not surprising that a lot of effort was and still is devoted to its reconciliation with the quantum mechanical description in terms of delocalized wave functions. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] One of the promising procedures which indeed seem to provide the desired link between the classical and quantum chemical description of chemical bonding is the approach based on the so-called electron localization function (ELF). [19][20][21][22] This function allows the unique partitioning of the molecule into disjunct domains, which indeed are reminiscent of classical chemical bonds.…”

Section: Introductionmentioning

confidence: 99%

Electron pairing and chemical bonds: Pair localization in ELF domains from the analysis of domain averaged Fermi holes

Ponec

Chaves

2006

J Comput Chem

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This article reports the application of a recently proposed formalism of domain averaged Fermi holes to the problem of the localization of electron pairs in electron localization function (ELF) domains and its possible implications for the electron pair model of chemical bond. The main focus was on the systems, such as H 2 O or N 2 , in which the ''unphysical'' population of ELF domains makes the parallel between these domains and chemical bond questionable. On the basis of the results of the Fermi-hole analysis, we propose that the above problems could be due to the fact that in some cases the boundaries of the ELF domains need not be determined precisely enough.

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“…Early applications of the VB theory used frozen atomic orbitals, whereas nowadays [81][82][83][84] both the spin-coupling coefficients c k and the orbitals can be variationally optimized, even when using a number of configurations in place of the single-orbital product appearing in Eq. ͑1͒.…”

mentioning

confidence: 99%

Understanding adsorption of hydrogen atoms on graphene

Casolo

Løvvik

Martinazzo

et al. 2009

The Journal of Chemical Physics

334

375

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Adsorption of hydrogen atoms on a single graphite sheet ͑graphene͒ has been investigated by first-principles electronic structure means, employing plane-wave based periodic density functional theory. A 5 ϫ 5 surface unit cell has been employed to study single and multiple adsorptions of H atoms. Binding and barrier energies for sequential sticking have been computed for a number of configurations involving adsorption on top of carbon atoms. We find that binding energies per atom range from ϳ0.8 to ϳ1.9 eV, with barriers to sticking in the range 0.0-0.15 eV. In addition, depending on the number and location of adsorbed hydrogen atoms, we find that magnetic structures may form in which spin density localizes on a ͱ 3 ϫ ͱ 3R30°sublattice and that binding ͑barrier͒ energies for sequential adsorption increase ͑decrease͒ linearly with the site-integrated magnetization. These results can be rationalized with the help of the valence-bond resonance theory of planar conjugated systems and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.

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Applications of spin-coupled valence bond theory

Cited by 292 publications

References 18 publications

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

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

Electron pairing and chemical bonds: Pair localization in ELF domains from the analysis of domain averaged Fermi holes

Understanding adsorption of hydrogen atoms on graphene

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