Calculation of ESR coupling constants by means of the unrestricted Hartree-Fock method

Hameka, Hendrik F.; Turner, Almon G.

doi:10.1016/0022-2364(85)90031-9

Cited by 10 publications

(7 citation statements)

References 12 publications

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“…For TiF 3 , the minimal CAS(1,5) comprises one electron in five 3d/4s hybrid orbitals. CAS (3,7) is augmented by titanium 1s and another 4s-rich orbital. For HgH and HgF, CAS (3,6) consists of three electrons in six orbitals with large 6s and 6p character.…”

Section: Computational Detailsmentioning

confidence: 99%

“…They also yield a sizable isotropic PSO component in the fluorine HFC without which the calculated SO result would be far from experiment. With CAS (1,7) the isotropic PSO contribution to the fluorine HFCC of NpF 6 is −18 MHz. The PSO term is reduced to −7 if spin polarization is introduced but the three bonding fluorine 2p σ combinations are excluded from the active space.…”

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confidence: 99%

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Effects from Spin–Orbit Coupling on Electron–Nucleus Hyperfine Coupling Calculated at the Restricted Active Space Level for Kramers Doublets

Sharkas

Pritchard

Autschbach

2015

J. Chem. Theory Comput.

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Calculations of electron-nucleus hyperfine coupling were implemented at the restricted active space state interaction (RASSI) level to treat spin-orbit (SO) coupling, based on scalar relativistic restricted active space wave functions. The current implementation is suitable for light atomic systems, for light ligand atoms in heavy metal complexes, and for spin-orbit coupling-induced hyperfine coupling of heavy atoms if the unpaired electrons are described by orbitals with high angular momentum. Spin polarization is reasonably well treated by allowing one hole and one electron in a window of active orbitals ('ras1', 'ras3') surrounding the principal active space ('ras2'). A benchmark set of Kramers doublet states of molecules with light and heavy atoms is used to evaluate the approach and verify the implementation. For NpF6, the impact of SO coupling on the Np and F hyperfine coupling tensors is investigated in detail. It is demonstrated that the Np hyperfine coupling is strongly dominated by SO effects, that there is a large SO effect on the F hyperfine tensor components, and that SO coupling causes the fluorine dipolar term to acquire an isotropic component.

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Section: Computational Detailsmentioning

confidence: 99%

mentioning

confidence: 99%

Effects from Spin–Orbit Coupling on Electron–Nucleus Hyperfine Coupling Calculated at the Restricted Active Space Level for Kramers Doublets

Sharkas

Pritchard

Autschbach

2015

J. Chem. Theory Comput.

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“…From the computational standpoint, the employed basis set should be flexible at the core region and capable of describing core level spin polarization accurately . The description of core-level spin polarization is catastrophic , with Hartree–Fock theory. Low-order perturbation theory (e.g., second-order many body perturbation theory, MP2) cannot rectify these major shortcomings, and highly correlated wavefunction approaches, such as coupled cluster (CC) theory with single and double excitations (CCSD), in their traditional forms are computationally too demanding to be applied to most real-life problems.…”

Section: Theorymentioning

confidence: 99%

A Joint Venture of Ab Initio Molecular Dynamics, Coupled Cluster Electronic Structure Methods, and Liquid-State Theory to Compute Accurate Isotropic Hyperfine Constants of Nitroxide Probes in Water

Sharma

Tran

Pongratz

et al. 2021

J. Chem. Theory Comput.

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The isotropic hyperfine coupling constant (HFCC, A iso) of a pH-sensitive spin probe in a solution, HMI (2,2,3,4,5,5-hexamethylimidazolidin-1-oxyl, C9H19N2O) in water, is computed using an ensemble of state-of-the-art computational techniques and is gauged against X-band continuous wave electron paramagnetic resonance (EPR) measurement spectra at room temperature. Fundamentally, the investigation aims to delineate the cutting edge of current first-principles-based calculations of EPR parameters in aqueous solutions based on using rigorous statistical mechanics combined with correlated electronic structure techniques. In particular, the impact of solvation is described by exploiting fully atomistic, RISM integral equation, and implicit solvation approaches as offered by ab initio molecular dynamics (AIMD) of the periodic bulk solution (using the spin-polarized revPBE0-D3 hybrid functional), embedded cluster reference interaction site model integral equation theory (EC-RISM), and polarizable continuum embedding (using CPCM) of microsolvated complexes, respectively. HFCCs are obtained from efficient coupled cluster calculations (using open-shell DLPNO-CCSD theory) as well as from hybrid density functional theory (using revPBE0-D3). Re-solvation of “vertically desolvated” spin probe configuration snapshots by EC-RISM embedding is shown to provide significantly improved results compared to CPCM since only the former captures the inherent structural heterogeneity of the solvent close to the spin probe. The average values of the A iso parameter obtained based on configurational statistics using explicit water within AIMD and from EC-RISM solvation are found to be satisfactorily close. Using either such explicit or RISM solvation in conjunction with DLPNO-CCSD calculations of the HFCCs provides an average A iso parameter for HMI in aqueous solution at 300 K and 1 bar that is in good agreement with the experimentally determined one. The developed computational strategy is general in the sense that it can be readily applied to other spin probes of similar molecular complexity, to aqueous solutions beyond ambient conditions, as well as to other solvents in the longer run.

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“…Typically, spin polarization contributions are too large by about a factor of 3. This has been analyzed in some detail by Hameka and Chipman . Thus, the calculation of accurate first principles spin densities requires the incorporation of a substantial amount of dynamic correlation.…”

Section: Introductionmentioning

confidence: 99%

Correlated ab Initio Spin Densities for Larger Molecules: Orbital-Optimized Spin-Component-Scaled MP2 Method

2010

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The performance of the orbital-optimized MP2 method (OO-MP2) and its spin-component-scaled variant is investigated for the prediction of atomic and molecular hyperfine coupling constants (hfccs). The calculated hfccs are compared to experimental as well as to CCSD(T) reference results. The OO-MP2 isotropic hfccs for a series of small radicals are almost of CCSD quality but are obtained with iterative O (N⁵) effort. The dipolar hfccs are less well predicted by the OO-MP2 methods, whereas spin-component scaling improves the description of the hyperfine structure. The spin contamination in the OO-MP2 wave function is drastically reduced compared to the standard unrestricted Hartree-Fock wave function. The applicability of the OO-MP2 to fairly large systems is demonstrated for the solvated p-benzosemiquinone radical anion, where calculations with almost 2000 basis functions have been performed.

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Calculation of ESR coupling constants by means of the unrestricted Hartree-Fock method

Cited by 10 publications

References 12 publications

Effects from Spin–Orbit Coupling on Electron–Nucleus Hyperfine Coupling Calculated at the Restricted Active Space Level for Kramers Doublets

Effects from Spin–Orbit Coupling on Electron–Nucleus Hyperfine Coupling Calculated at the Restricted Active Space Level for Kramers Doublets

A Joint Venture of Ab Initio Molecular Dynamics, Coupled Cluster Electronic Structure Methods, and Liquid-State Theory to Compute Accurate Isotropic Hyperfine Constants of Nitroxide Probes in Water

Correlated ab Initio Spin Densities for Larger Molecules: Orbital-Optimized Spin-Component-Scaled MP2 Method

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