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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9756-9763 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine (hf) structures of radical cations are calculated using first principles density functional theory. Within the local spin density (LSD) approximation, the isotropic hyperfine coupling constants (Fermi contact terms) are computed for a set of linear (nonbranched) alkane and alkene radical cations with up to four carbon atoms. The results are as a whole in very good agreement with experimental data, obtained from low temperature matrix isolation electron-spin resonance (ESR) measurements, and with results from previous configuration interaction calculations.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3674-3678 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine structure of the 14NH2 radical is investigated by means of multireference single and double configuration interaction (MRCI) techniques. Particular attention is paid to the dependence of the coupling constants on the basis set, reference space, and configuration selection energy threshold. It is found that convergence can be obtained only if more than 83 reference configurations are included with an energy threshold of at least 10−7 hartree. With up to 126 reference configurations, an energy threshold smaller than 10−8 hartree and an uncontracted (13s8p2d/8s2p) basis set, the MRCI isotropic couplings (27.44 and −68.47 MHz for N and H, respectively) are in very good agreement with experimental data (27.9 and −67.2 MHz, respectively). © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1050-1056 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equilibrium geometries, energetics, and hyperfine coupling constants for a number of charged magnesium clusters and magnesium–rare gas complexes are investigated using gradient corrected density functional theory. In the study of matrix effects, Mg+ and Mg+2 are embedded in matrices with up to 10 neon or argon atoms. For the magnesium ion, we calculate a shift in the isotropic hyperfine coupling constant of 10 G when changing the matrix from Ne to Ar (expt. value: 10.9 G), and for Mg+2 the calculated shift is −0.5 G (expt. value=1.1 G). In the second part of the paper, several different positively charged magnesium clusters with up to six magnesium atoms are optimized, and the resulting geometries, relative energies, and hyperfine coupling constants are compared with experimental data and with previous theoretical studies. Based on the computed averaged hyperfine coupling constants, a reassignment is proposed of the experimentally observed average values (in gauss), −222.5 (Mg+), −105.4 (Mg+2), −69.5 (linear Mg+3), −55.0 (triangular Mg+3), −48.5 (Mg+4), and −34.6 (Mg+5). The corresponding calculated values are −211.6, −100.0, −65.2, −58.7, −48.3, and −33.3 G, respectively. For the hexamer ion, we predict an average hfcc of −28.5 G. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8166-8173 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermal motion of CD+4 in the gas phase at 4 and 40 K is studied by means of a molecular dynamics method using the MP2/6-31G(d,p) force field. The thermal motion of CD+4 in the temperature range from 4 to 40 K does not involve a deuterium permutation on the picosecond time scale. The electronic energy fluctuations of CD+4 due to thermal motion are less than 0.7 kcal/mol at 4 K and 1.6 kcal/mol at 40 K, which is less than the energy barrier (3.4 kcal/mol at MP2 level) required for the permutation between two energy minimum C2v structures. On the basis of these calculations it is suggested that the observation of four equivalent hydrogen atoms in the ESR spectrum of CH+4 can be attributed to fast quantum tunneling, with an estimated rate of 4.3×106 s−1 for CH+4 and 1.6×103 s−1 for CD+4. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 872-878 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density functional theory with gradient corrections (DFTG) is applied to a series of second-row transition metal compounds. The mean absolute deviations from experiment for the atomic excitation energies and ionization potential are in the range 0.2–0.4 eV. In comparison with accurate multireference configuration interaction (MR-CI) and parametrized CI with parameter 80 (PCI-80) results for the binding energies of the MCH+2 cations, the mean absolute deviation is 6.7 kcal/mol to be compared with 17.8 kcal/mol at the modified coupled pair functional (MCPF) level. The DFTG result is more sensitive to the choice of asymptote with a mean deviation of 14 kcal/mol if the bonding atomic state is not used as asymptote. Product energies and transition states for the addition of methane to RhXL (X=H, Cl, L=H2O, NH3, PH3, and CO) also show the same trends as the PCI-80 comparison and represent an improvement over the MCPF results. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5066-5075 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isotropic and anisotropic hyperfine (hf) structures of a set of anionic, neutral and cationic radicals are investigated by means of local and nonlocal gradient-corrected density functional theory (DFT). The molecules under study are formed by H, C, N, O, F, and Cl atoms, and the hf structures are computed at both the experimental (where present) and various DFT and CI optimized geometries. The agreement with experiment and with results from previous CI or MRCI calculations is generally very satisfactory. The anisotropic hf couplings are relatively insensitive to basis set effects and functional form, whereas the isotropic hf couplings are highly dependent on the form of the nonlocal corrections to the exchange functional, particularly for heteroatoms. Using the functional by Perdew and Wang ("PW86''), an excellent agreement with experiment is obtained for all neutral and cationic radicals, whereas for the halide containing anions somewhat elongated bond lengths, and thus less accurate hf structures, are obtained.
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 11969-11973 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 12215-12219 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 12737-12741 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 12742-12744 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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