Symmetry breaking in molecular calculations and the reliable prediction of equilibrium geometries. The formyloxyl radical as an example

McLean, A. D.; Lengsfield, Byron H.; Pacansky, J.; Ellinger, Y.

doi:10.1063/1.449162

Cited by 155 publications

(93 citation statements)

References 21 publications

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“…In some of these species, e.g., core-ionized diatoms, the use of a single configuration method leads to the so-called ''symmetry dilemma.'' 59 The symmetry dilemma was analyzed in VB terms by McLean, 60 and shown to arise from a competition between two effects. One is the familiar resonance effect by which a mixture of two resonance structures is lower in energy than either one taken separately.…”

Section: The Spin-coupled Valence Bond Methodsmentioning

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: The Spin-coupled Valence Bond Methodsmentioning

confidence: 99%

A survey of recent developments in ab initio valence bond theory

Hiberty

Shaik

2006

J Comput Chem

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“…[8][9][10] It also presents theoretical challenges owing to its two low-lying excited states, which strongly mix and result in a strong pseudo-Jahn-Teller (PJT) coupling that may or may not distort the ground-state equilibrium geometry from C 2V symmetry. [11][12][13][14][15][16] This coupling renders the accurate computation of the geometry and vibronic structure of this species difficult. In this paper, we characterize the vibronic structure of the HCO 2 and DCO 2 radicals using slow photoelectron velocity-map imaging (SEVI) 17 in combination with a theoretical treatment using a quasidiabatic Hamiltonian approach parametrized by high-level ab initio calculations.…”

Section: Introductionmentioning

confidence: 99%

Vibronic Structure of the Formyloxyl Radical (HCO₂) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

et al. 2009

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We report high-resolution photoelectron spectra of HCO 2 -and DCO 2 -obtained with slow photoelectron velocity-map imaging. Well-resolved photodetachment transitions to the 2 A 1 and 2 B 2 states of the neutral radicals were observed. In addition, vibronic levels of the HCO 2 and DCO 2 radicals with up to 2000 cm -1 of internal energy were calculated using a quasidiabatic Hamiltonian approach and high-level ab initio calculations. Spectral simulations using the calculated levels were found to be in excellent agreement with the experimental spectra and used to assign many of its features. This study unambiguously determined that the 2 A 1 state is the ground state of both HCO 2 and DCO 2 , in contrast to earlier work that indicated the 2 B 2 state was the ground state for DCO 2 . For both isotopologs, the 2 B 2 state is a very low-lying excited state with term energies of T 0 ) 318 ( 8 cm -1 for HCO 2 and T 0 ) 87 ( 8 cm -1 for DCO 2 . The adiabatic electron affinities are determined to be EA(HCO 2 ) ) 3.4961 ( 0.0010 eV and EA(DCO 2 ) ) 3.5164 ( 0.0010 eV.

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“…A commonly encountered problem comes from lone pairs. 98,99 None of these approaches can thus be considered as a panacea. Consequently, any way of designing an efficient but "small enough" zeroth-order variational space for further MRCI or MRPT calculations seems thus welcomed.…”

Section: Application: Designing Zeroth-order Variational Spaces Fomentioning

confidence: 99%

Singlet-triplet gaps in large multireference systems: Spin-flip-driven alternatives for bioinorganic modeling

Lande

Moliner²,

Parisel³

2007

The Journal of Chemical Physics

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The proper description of low-spin states of open-shell systems, which are commonly encountered in the field of bioinorganic chemistry, rigorously requires using multireference ab initio methodologies. Such approaches are unfortunately very CPU-time consuming as dynamic correlation effects also have to be taken into account. The broken-symmetry unrestricted (spin-polarized) density functional theory (DFT) technique has been widely employed up to now to bypass that drawback, but despite a number of relative successes in the determination of singlet-triplet gaps, this framework cannot be considered as entirely satisfactory. In this contribution, we investigate some alternative ways relying on the spin-flip time-dependent DFT approach [Y. Shao et al. J. Chem. Phys. 118, 4807 (2003)]. Taking a few well-documented copper-dioxygen adducts as examples, we show that spin-flip (SF)-DFT computed singlet-triplet gaps compare very favorably to either experimental results or large-scale CASMP2 computations. Moreover, it is shown that this approach can be used to optimize geometries at a DFT level including some multireference effects. Finally, a clear-cut added value of the SF-DFT computations is drawn: if pure ab initio data are required, then the electronic excitations revealed by SF-DFT can be considered in designing dramatically reduced zeroth-order variational spaces to be used in subsequent multireference configuration interaction or multireference perturbation treatments.

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Symmetry breaking in molecular calculations and the reliable prediction of equilibrium geometries. The formyloxyl radical as an example

Cited by 155 publications

References 21 publications

A survey of recent developments in ab initio valence bond theory

A survey of recent developments in ab initio valence bond theory

Vibronic Structure of the Formyloxyl Radical (HCO₂) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

Singlet-triplet gaps in large multireference systems: Spin-flip-driven alternatives for bioinorganic modeling

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Symmetry breaking in molecular calculations and the reliable prediction of equilibrium geometries. The formyloxyl radical as an example

Cited by 155 publications

References 21 publications

A survey of recent developments in ab initio valence bond theory

A survey of recent developments in ab initio valence bond theory

Vibronic Structure of the Formyloxyl Radical (HCO2) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations

Singlet-triplet gaps in large multireference systems: Spin-flip-driven alternatives for bioinorganic modeling

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Vibronic Structure of the Formyloxyl Radical (HCO₂) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations