Orthogonal Valence Bond Hamiltonians incorporating dynamical correlation effects

Giner, Emmanuel; Angeli, Celestino; Scemama, Anthony; Malrieu, Jean‐Paul

doi:10.1016/j.comptc.2017.03.001

Cited by 5 publications

(3 citation statements)

References 35 publications

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“…Explaining this observation would require further analysis, e.g., by invoking the valence bond picture. 53,54 As the geometries of the stationary points demonstrate, the BLA, a-twist and b-twist are the main coordinates driving the relaxation of the pCTM À chromophore in the S 1 excited state. If the QnBR energy is lower than VEE, the initial relaxation from the FC point involves the BLA coordinate followed by the a-twist.…”

Section: Energies Of the Resonance Structures -Impact On The S 1 -Stamentioning

confidence: 99%

Four resonance structures elucidate double-bond isomerisation of a biological chromophore

Gromov

Domratcheva

2020

Phys. Chem. Chem. Phys.

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Section: Energies Of the Resonance Structures -Impact On The S 1 -Stamentioning

confidence: 99%

Four resonance structures elucidate double-bond isomerisation of a biological chromophore

Gromov

Domratcheva

2020

Phys. Chem. Chem. Phys.

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“…Other methods use orthogonalized atomic orbitals, which also bear delocalization tails, and nodes created by the orthogonalization constraint. 8 Here, we define all the active orbitals as purely atom-centered, without any delocalization tails or spurious nodes, so as to ensure a clear correspondence between the mathematical expressions of the VB structures and their physical meanings, ionic or covalent. In general, the VB orbitals {φ p } are expressed as a linear combination of basis functions {χ μ } that says…”

Section: ■ Introductionmentioning

confidence: 99%

“…However, some methods like generalized VB or spin-coupled VB methods use a semilocalized option, whereby a bond is described as a singlet coupling between two electrons in nonorthogonal orbitals that possess usually small delocalization tails resulting from the variational orbital optimization. Other methods use orthogonalized atomic orbitals, which also bear delocalization tails, and nodes created by the orthogonalization constraint . Here, we define all the active orbitals as purely atom-centered, without any delocalization tails or spurious nodes, so as to ensure a clear correspondence between the mathematical expressions of the VB structures and their physical meanings, ionic or covalent.…”

Section: Introductionmentioning

confidence: 99%

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Braı̈da

Chen

et al. 2020

J. Chem. Theory Comput.

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A novel state-averaged version of ab initio nonorthogonal valence bond method is described, for the sake of accurate theoretical studies of excited states in the valence bond framework. With respect to standard calculations in the molecular orbital framework, the state-averaged breathingorbital valence bond (BOVB) method has the advantage to be free from the penalizing constraint for the ground and excited state(s) to share the same unique set of orbitals. The ability of the BOVB method to faithfully describe excited states and to compute accurate transition energies from the ground state is tested on the five lowest-lying singlet electronic states of ozone and sulfur dioxide, among which 1 1 B 2 and 2 1 A 1 are the challenging ones. As the 1 1 A 2 , 1 1 B 1 , and 1 1 B 2 states are of different symmetries than the ground state, they can be calculated at the state-specific BOVB level. On the other hand, the 2 1 A 1 states and the 1 1 A 1 ground states, which are of like symmetry, are calculated with the state-averaged BOVB technique. In all cases, the calculated vertical energies are close to the experimental values when available, and at par with the most sophisticated calculations in the molecular framework, despite the extreme compactness of the BOVB wave functions, made of no more than 5−9 valence bond structures in all cases. The features that allow the combination of compactness and accuracy in challenging cases are analyzed. For the "ionic" 1 1 B 2 states, which are the site of important charge fluctuations, it is because of the built-in dynamic correlation inherent to the BOVB method. For the 2 1 A 1 ones, this is the fact that these states have the degree of freedom of having different orbitals than the ground states, even though they are of like symmetry and calculated simultaneously using the newly implemented state-average BOVB algorithm. Finally, the description of the excited states in terms of Lewis structures is insightful, rationalizing the fast ring closure for the 2 1 A 1 state of ozone and predicting some diradical character in the socalled "ionic" 1 1 B 2 states.

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Orthogonal Valence Bond as a Bridge Between the Valence Bond and Molecular Orbital Representations of the Wave Function

Angeli¹,

Guihéry²,

Malrieu³

2024

Comprehensive Computational Chemistry

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Orthogonal Valence Bond Hamiltonians incorporating dynamical correlation effects

Cited by 5 publications

References 35 publications

Four resonance structures elucidate double-bond isomerisation of a biological chromophore

Four resonance structures elucidate double-bond isomerisation of a biological chromophore

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Orthogonal Valence Bond as a Bridge Between the Valence Bond and Molecular Orbital Representations of the Wave Function

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