Second-order perturbation theory with a complete active space self-consistent field reference function

Andersson, Kerstin; Malmqvist, Per‐Åke; Roos, Björn O.

doi:10.1063/1.462209

Cited by 3,535 publications

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“…CASPT2 single-point energy corrections (using the same active space) were computed at the CASSCF geometries, using a level shift to eliminate intruder states and reduce a systematic bias in the method favoring high spin states. 41 The basis set employed was the flexible ANO-L basis set of Widmark et al, of polarized valence triple-ζ (pVTZ) quality. 42 All the CASPT2/CASSCF calculations were performed using the Molcas 6.2 software suite.…”

Section: ' Computational Methodsmentioning

confidence: 99%

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

Hanway

Winter

2011

J. Am. Chem. Soc.

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The geometries and energies of the electronic states of phenyloxenium ion 1 (Ph−O + ) were computed at the multireference CASPT2/pVTZ level of theory. Despite being isoelectronic to phenylnitrene 4, the phenyloxenium ion 1 has remarkably different energetic orderings of its electronic states. The closed-shell singlet configuration ( 1 A 1 ) is the ground state of the phenyloxenium ion 1, with a computed adiabatic energy gap of 22.1 kcal/mol to the lowest-energy triplet state ( 3 A 2 ). Open-shell singlet configurations ( 1 A 2 , 1 B 1 , 1 B 2 , 2 1 A 1 ) are significantly higher in energy (>30 kcal/mol) than the closed-shell singlet configuration. These values suggest a revision to the current assignments of the ultraviolet photoelectron spectroscopy bands for the phenoxy radical to generate the phenyloxenium ion 1. For para-substituted phenyloxenium ions, the adiabatic singlet−triplet energy gap (ΔE ST ) is found to have a positive linear free energy relationship with the Hammett-like σ + R /σ + substituent parameters; for meta substituents, the relationship is nonlinear and negatively correlated. CASPT2 analyses of the excited states of p-aminophenyloxenium ion 5 and pcyanophenyloxenium ion 10 indicate that the relative orderings of the electronic states remain largely unperturbed for these para substitutions. In contrast, meta-donor-substituted phenyloxenium ions have lowenergy open-shell states (open-shell singlet, triplet) due to stabilization of a π,π* diradical state by the donor substituent. However, all of the other phenyloxenium ions and larger aryloxenium ions (naphthyl, anthryl) included in this study have closed-shell singlet ground states. Consequently, ground-state reactions of phenyloxenium ions are anticipated to be more closely related to closed-shell singlet arylnitrenium ions (Ar−NH + ) than their isoelectronic arylnitrene (Ar−N) counterparts. Disciplines Materials Chemistry | Other Chemistry | Physical Chemistry CommentsReprinted (adapted) with permission from J. Am. Chem. Soc., 2011, 133 (13) Oxenium ions are hypovalent species of formula R-O þ . These reactive intermediates are isoelectronic with nitrenes, with a formally monovalent oxygen containing two nonbonding electron pairs. Like nitrenes, the electron-deficient nature of these intermediates makes them powerful electrophiles, further amplified by the formal positive charge on the electronegative oxygen. These species are increasingly being proposed as intermediates in useful umpolung synthetic transformations, such as the oxidative Hosomi-Sakurai reaction, 1,2 the oxidative Wagner-Meerwin transposition, 3 electrochemical oxidations of phenols and phenolates, 4,5 alkane oxidations, 6 and a wide variety of other phenolic oxidations and tautomerization reactions. 7-11 These reactions convert phenols and alkanes, many of which are derived from petrochemical feedstocks, into value-added products such as cyclohexadienones, substituted phenols, and oxidized alkanes, as well as petrochemicals like poly(1,4-phenylene ether), a high-va...

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Section: ' Computational Methodsmentioning

confidence: 99%

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

Hanway

Winter

2011

J. Am. Chem. Soc.

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“…17 The complete active space (CAS) SCF method 11 was used to generate molecular orbitals and reference functions for subsequent multiconfigurational second order perturbation calculations of the dynamic correlation energy (MS-CASPT2). [12][13][14] The multistate option (MS) of the CASPT2 method was used. This is a new feature of MOLCAS-5.2 that allows CASPT2 calculations to be performed for a number of the selected roots from a state average CASSCF calculation.…”

Section: Methods and Details Of The Calculationsmentioning

confidence: 99%

“…These calculations were performed using multiconfigurational (CAS) SCF theory 11 with dynamic correlation effects added using second order perturbation theory (CASPT2). [12][13][14] Relativistic effective core potentials (ECP) were used and no spin-orbit effects were included. The equilibrium structure of the OUO molecule was later determined 15 using the same approach together with a new method (CASSI-SO) to treat spin-orbit coupling.…”

Section: Introductionmentioning

confidence: 99%

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

Gagliardi¹,

Manna²,

Roos³

2003

Faraday Disc.

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An attempt has been made to study the reaction between a uranium atom and a nitrogen molecule theoretically using multiconfigurational wave functions. The C 2v part of the reaction surface has been computed for several electronic states of various spin multiplicities. The system proceeds from a neutral uranium atom in its (5f) 3 (6d)(7s) 2 , 5 L ground state to the linear molecule NUN, which has a 1 S þ g ground state and uranium in a formal U(VI) oxidation state. The effect of spin-orbit coupling has been estimated at crucial points along the reaction. These preliminary results shows that the system proceeds from a quintet state for U + N 2 , via a triplet transition state to the final closed shell molecule. An eventual energy barrier for the insertion reaction is caused by the spin-orbit coupling energy.

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“…[12][13][14] Scalar relativistic effects were included via a Douglas-Kroll (DK) Hamiltonian. 15,16 The effects of spin-orbit (SO) coupling were calculated employing a newly developed method based on the CASSCF state interaction method (CASSI).…”

Section: Details Of the Calculationsmentioning

confidence: 99%

The Electronic Spectrum of Re₂Cl₈²^-: A Theoretical Study

Gagliardi¹,

Roos²

2003

Inorg. Chem.

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113

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One of the prototype compounds for metal−metal multiple bonding, the Re 2 Cl 8 2-ion, has been studied theoretically using multiconfigurational quantum chemical methods. The molecular structure of the ground state has been determined. It is shown that the effective bond order of the Re−Re bond is close to three, due to the weakness of, in particular, the δ bond. The electronic spectrum has been calculated with the inclusion of spin−orbit coupling. Observed spectral features have been reproduced with good accuracy, and a number of new assignments are suggested.

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Second-order perturbation theory with a complete active space self-consistent field reference function

Cited by 3,535 publications

References 23 publications

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

The Electronic Spectrum of Re₂Cl₈²^-: A Theoretical Study

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Second-order perturbation theory with a complete active space self-consistent field reference function

Cited by 3,535 publications

References 23 publications

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

Phenyloxenium Ions: More Like Phenylnitrenium Ions than Isoelectronic Phenylnitrenes?

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

The Electronic Spectrum of Re2Cl82-: A Theoretical Study

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Product

Resources

About

The Electronic Spectrum of Re₂Cl₈²^-: A Theoretical Study