Quantum Chemical Approaches to Treat Mixed‐Valence Systems Realistically for Delocalized and Localized Situations

Kaupp, Martin

doi:10.1002/9783527835287.ch3

Cited by 2 publications

(2 citation statements)

References 98 publications

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“…in the case of hydrogen bonding to MV radical anions. [1][2][3][4] The LR-SCS-CC2/aug-cc-pVTZ energy of DMP-L * relative to DMP-D * (23 kJ/mol) underestimates somewhat the experimental estimate of 32 ± 4 kJ/mol obtained from thermal populations. 8 As the energy difference from EOM-CCSD/aug-cc-pVTZ single-point calculations is 28 kJ/mol, this is likely due to the limited treatment of dynamical correlation by SCS-CC2.…”

Section: Investigation Of the Dmp Rydberg Statementioning

confidence: 81%

“…The literature on this topic is too vast to do justice here, and we refer the reader to some reviews and books. [1][2][3][4] Almost all spectroscopic studies are carried out in polar solvent environments, due to the fact that MV systems are often charged (radical) species that do not dissolve readily in nonpolar solvents. Such polar solvents, however, favor charge localization due to electrostatic interactions.…”

Section: Introductionmentioning

confidence: 99%

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Rydberg Electron Stabilizes the Charge Localized State of the Diamine Cation

Reimann

Sebastiani

Kirsch

et al. 2023

Preprint

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The interpretation of Rydberg spectra of gaseous dimethylpiperidine (DMP) as showing the co-existence of a localized and delocalized mixed-valent DMP+ radical cation has generated a controversial discussion about the performance of various electronic-structure methods. We revisit this discussion by high-level computations. An apparent barrier separating localized and delocalized DMP+ minima at MRCI+Q and a few other levels reflects unphysical curve crossings of the reference wave functions. These discontinuities on the surface are removed in state-averaged MRCI+Q calculations, as well as at IP-EOM-CCSD or CCSD(T) levels. This has prompted a high-level computational study of the actually observed Rydberg state of neutral DMP. Indeed, the 3s-type Rydberg electron binds more strongly to a localized rather than to a delocalized positive charge distribution. This stabilizes the localized structure to the extent where it becomes a local minimum for the DMP∗ Rydberg state, in contrast to DMP+, explaining the experimental observations. This appears to be the first case where interactions of a Rydberg electron with the underlying cationic core alter molecular structure in such a fundamental way.

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Section: Investigation Of the Dmp Rydberg Statementioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Rydberg Electron Stabilizes the Charge Localized State of the Diamine Cation

Reimann

Sebastiani

Kirsch

et al. 2023

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

Rydberg electron stabilizes the charge localized state of the diamine cation

Reimann,

Kirsch,

Sebastiani

et al. 2024

Nat Commun

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A previous controversial discussion regarding the interpretation of Rydberg spectra of gaseous dimethylpiperazine (DMP) as showing the co-existence of a localized and delocalized mixed-valent DMP+ radical cation is revisited. Here we show by high-level quantum-chemical calculations that an apparent barrier separating localized and delocalized DMP+ minima in previous multi-reference configuration-interaction (MRCI) calculations and in some other previous computations were due to unphysical curve crossings of the reference wave functions. These discontinuities on the surface are removed in state-averaged MRCI calculations and with some other, orthogonal high-level approaches, which do not provide a barrier and thus no localized minimum. We then proceed to show that in the actually observed Rydberg state of neutral DMP the 3s-type Rydberg electron binds more strongly to a localized positive charge distribution, generating a localized DMP* Rydberg-state minimum, which is absent for the DMP+ cation. This work presents a case where interactions of a Rydberg electron with the underlying cationic core alter molecular structure in a fundamental way.

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Quantum Chemical Approaches to Treat Mixed‐Valence Systems Realistically for Delocalized and Localized Situations

Cited by 2 publications

References 98 publications

Rydberg Electron Stabilizes the Charge Localized State of the Diamine Cation

Rydberg Electron Stabilizes the Charge Localized State of the Diamine Cation

Rydberg electron stabilizes the charge localized state of the diamine cation

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