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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3292-3300 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic g-tensors parametrize the Zeeman splitting observed in the EPR spectra of radicals. In this work, we report g-tensor calculations for NO2, H2O+, and CO+ at the multireference CI level. Deviations of the tensor elements (g-shifts) from the free-electron value are computed via a perturbation expansion, complete to second order in relevant Breit–Pauli terms. The g-shifts we obtain for these molecules are as follows: NO2: Δgxx=3571, Δgyy=−10296, Δgzz=−537; H2O+: Δgxx=−249, Δgyy=15733, Δgzz=4105; CO+: Δg⊥=−2383, Δg(parallel)=−181 [all values in parts per million (ppm)]. These results are in reasonable agreement with gas phase experimental data. Larger g-shifts are typically within 20% of experiment, whereas smaller g-shifts generally differ by no more than several hundred ppm. Basis set effects and gauge dependence are examined in the case of CO+. For this molecule, a good valence description is vital for achieving accurate Δg-values and small gauge-dependence. Polarization functions are of some use in these calculations, but diffuse functions have little effect on the gauge dependence of a cationic radical such as CO+. Vibrational effects are also examined for CO+. The vibrationally averaged g⊥-shift only differs from the equilibrium value by 83 ppm. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 93 (1996), S. 259-267 
    ISSN: 1432-2234
    Keywords: Electronicg-tensor ; Zeeman effect ; Gauge invariance ; Hartree-Fock wavefunctions ; Magnetic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electronicg-tensors for NO2, CO+ and H2O+ are calculated at the restricted open-shell Hartree-Fock (ROHF) level using the Rayleigh-Schrödinger perturbation approach. All known first- and second-order contributions have been evaluated, including the relativistic mass correction, one- and two-electron spin Zeeman gauge correction terms, and one- and two-electron second-order terms. Substantial code development has been necessary, including an integral routine for computing the two-electron spin-Zeeman gauge correction term. Calculations have been done using triple zeta and quadruple zeta basis sets with additional polarization and semi-diffuse functions. Effective gauge invariance is obtained by placing the gauge origin at the molecule's electronic charge centroid. Excited state energies in the sum-over-states expansion are expressed using determinantal energies, thus avoiding the non-uniqueness of ROHF eigenvalues. Our results successfully reproduce trends in gas phaseg-shifts (δg=g−g e). However, discrepancies between our calculatedg-shifts and experimental ones, sometimes on the order of 50%, point to the need for a correlated treatment.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretica chimica acta 93 (1996), S. 259-267 
    ISSN: 0040-5744
    Keywords: Key words: Electronic g-tensor ; Zeeman effect ; Gauge invariance ; Hartree ; Fock wavefunctions ; Magnetic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  The electronic g-tensors for NO2, CO+ and H2O+ are calculated at the restricted open-shell Hartree–Fock (ROHF) level using the Rayleigh–Schrödinger perturbation approach. All known first- and second-order contributions have been evaluated, including the relativistic mass correction, one- and two-electron spin Zeeman gauge correction terms, and one- and two-electron second-order terms. Substantial code development has been necessary, including an integral routine for computing the two-electron spin-Zeeman gauge correction term. Calculations have been done using triple zeta and quadruple zeta basis sets with additional polarization and semi-diffuse functions. Effective gauge invariance is obtained by placing the gauge origin at the molecule’s electronic charge centroid. Excited state energies in the sum-over-states expansion are expressed using determinantal energies, thus avoiding the non-uniqueness of ROHF eigenvalues. Our results successfully reproduce trends in gas phase g-shifts (Δg=g−g e). However, discrepancies between our calculated g-shifts and experimental ones, sometimes on the order of 50%, point to the need for a correlated treatment.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 36 (1996), S. 301-309 
    ISSN: 1434-6079
    Keywords: 33.45.B ; 31.10 ; 31.20.E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron-spin magnetic moments, in the form ofg-shifts, have been computed at the ROHF level for theX 2∑+ states of LiH+, BeH2+, LiH−, BeH and BH+. A perturbative approach, complete to second-order in appropriate Breit-Pauli operators, has been used. Retention of two-centre integrals has proven vital. First-order terms are important, especially in describing the negativeg ∥ shifts observed experimentally in2∑+ molecules. The relativistic mass correction dominates in first-order, except for LiH− where the two-electron spin-Zeeman gauge correction supersedes. Second-order terms contribute negatively, and only to the Δg ⊥ component. Along the isoelectronic series LiH− → BeH → BH+, the magnitude of Δg ⊥ increases due to the dependence of spin-orbit coupling on nuclear charge. The relation ofg-shifts to electronic structure and bonding is explored.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 1679-1684 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Despite their importance in the characterization of molecular magnetism, electronic g-tensors have received rather little theoretical attention. In this work, however, the ground-state g-tensor of MgF is computed at both the ROHF and multireference CI levels. The calculations are expanded complete to second order in appropriate Breit-Pauli terms and the contributions of all important magnetically coupled excited states are accounted for. Both the CI- and ROHF-level Δg∥-values (-59 and -55 ppm, respectively) are in agreement with experiment (-319 ± 500 ppm) within the range of experimental uncertainty. For Δg⊥, however, the ROHF treatment yields a value (-659 ppm) in substantial disagreement with experiment (-1319 ± 500 ppm). Fortunately, this discrepancy is alleviated by CI level treatment (Δg⊥ = -1447 ppm). © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 377-392 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular g-tensors for the molecules NO2, CO2-, C3H5, H2CO+, and NF3+ are calculated at the unrestricted Hartree-Fock (UHF) level using the Rayleigh-Schrödinger perturbation approach. All one-electron terms have been evaluated, including the relativistic mass correction, the one-electron spin-Zeeman gauge correction, and a second-order term involving the spin-orbit coupling and the orbital-Zeeman interaction. The relative importance of the first-order terms is found to be quite substantial. For first-row molecules, their total contribution is often of the same order of magnitude as of the second-order contribution, in some instances even larger. A study on the basis-set dependence of these g-tensors has been conducted. At this level, the most important basis-set criterion is shown to be a satisfactory description of the valence regions. Finally, the gauge dependence of these g-tensor calculations has been systematically studied. This dependence seems to be substantially reduced for basis sets which include polarization functions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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