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  • 1
    ISSN: 1432-2234
    Keywords: Key words: NMR parameters ; Spin-spin coupling constants ; Second-order polarization propagator approximation ; Second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes ; Basis set
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. We present correlated calculations of the indirect nuclear spin-spin coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes – SOPPA(CCSD). Attention is given to the effect of the so-called W 4 term, which has not been included in previous SOPPA spin-spin coupling constant studies of these molecules. Large sets of Gaussian basis functions, optimized for the calculation of indirect nuclear spin-spin coupling constants, were used instead of the in general rather small basis sets used in previous studies. We find that for nearly all couplings the SOPPA(CCSD) method performs better than SOPPA.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2234
    Keywords: Polarization propagator ; SOPPA ; Dynamic polarizability ; Depolarization ratio ; Dipole moment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We report values of the correlated dynamic dipole polarizability for the halides HX and CH3X (X = F, Cl and Br). The polarizabilities are calculated within the second-order polarization propagator approximation (SOPPA). The correlated results are in much better agreement with the available experimental results, compared to RPA. We also report the second-order dipole moments using both the “relaxed” and “unrelaxed” MP2 density matrices. The relaxed results are in better agreement with experiment.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2234
    Keywords: Magnetic shieldings ; Ab initio ; Polarization propagator methods ; SOPPA ; Gauge origin invariant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We have applied a gauge origin invariant method for calculations of nuclear magnetic shielding constants to the singly bonded molecules BF, F2, BH3, CH4, NH3, H2O, and HF as well as to the1H shielding constants of HCN and C2H2. The calculations were performed at the RPA and second order polarization propagator (SOPPA) level of theory. For most molecules the correlation contribution in SOPPA is less diamagnetic than in the comparable MP2 calculations. For F2, SOPPA gives a large paramagnetic correlation correction whereas the MP2 method gives a very small correlation contribution. For all molecules agreement with experimental results is generally improved at the SOPPA level compared to RPA. We have also demonstrated that second order gauge origin invariant, common and local origin (SOLO) methods do not necessarily give the same shielding even in the limit of a converged basis set.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8969-8975 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second order polarization propagator approximation (SOPPA) has been applied to the calculation of the dynamic dipole polarizability, α(ω), of the molecules N2, C2H2, CO, and HCN. The dipole oscillator sum rules S(−4) and S(−6), which are the leading contributions to the Cauchy expansion of the polarizability, have also been evaluated at SOPPA level, using a polynomial fit to this expansion. These are the first reported values of the higher sum rules obtained using the SOPPA approach, and we observe excellent agreement with experiment. We also discuss the applicability of scaling or additivity expressions for obtaining the correlated polarizability from static correlated and dynamic uncorrelated quantities.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
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  • 6
    ISSN: 1432-2234
    Keywords: Key words: PbH4 ; NMR parameters ; Spin ; spin coupling constants ; Basis set ; Multiconfigurational linear response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. We report ab initio calculations of the indirect nuclear spin–spin coupling constants of PbH4 using a basis set which was specially optimized for correlated calculations of spin–spin coupling constants. All nonrelativistic contributions and the most important part of the spin–orbit correction were evaluated at the level of the random phase approximation. Electron correlation corrections to the coupling constants were calculated with the multiconfigurational linear-response method using extended complete and restricted active space wavefunctions as well as with the second-order polarization propagator approximation and the second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes. The effects of nuclear motion were investigated by calculating the coupling constants as a function of the totally symmetric stretching coordinate. We find that the Fermi contact term dominates the Pb‐H coupling, whereas for the H‐H coupling it is not more important than the orbital paramagnetic and diamagnetic contributions. Correlation affects mainly the Fermi contact term. Its contribution to the one-bond coupling constant is reduced by correlation, independent of the method used; however, the different correlated methods give ambiguous results for the Fermi contact contribution to the H‐H couplings. The dependence of both coupling constants on the Pb‐H bond length is dominated by the change in the Fermi contact term. The geometry dependence is, however, overestimated in the random phase approximation.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 487-495 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Verdet constant (V), which governs magnetic optical rotation, has been evaluated, at several frequencies, as a quadratic response function for H2, N2, CO, and FH, in the random-phase approximation (RPA). At the same time, the "normal'' Verdet constant (VN) has been found from the linear response function in both RPA and second-order polarization propagator approximations (SOPPA), though in the latter case only for a single frequency. For H2 and N2, V is in good agreement with experiment, and the ratio V/VN accords very well with other accurate results. For CO the effect of correlation turns out to be more important. For FH there are no other results for V with which we can compare; however, SOPPA calculations on the normal Verdet constant show a dramatic effect for electron correlation. It appears that V/VN (which in all cases is only slightly dependent on frequency) is close to unity for FH, thus ruling out a connection between this ratio and molecular polarity. Zero-point-vibrational averaging is taken into account in the calculations and the effect of shifting the origin of the gauge is discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9748-9757 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the potential temperature independent van Vleck paramagnetism of closed shell diatomic hydrides with six valence electrons. More specifically, we have studied the magnetizability of the first row hydrides BeH−, BH, CH+, of the second row hydrides MgH−, AlH, and SiH+, and of the third row hydride GeH+. The magnetizability was calculated using a gauge origin independent method at the uncorrelated SCF level within the random-phase approximation (RPA) as well as at different correlated levels within the second-order polarization propagator approximation (SOPPA) or various coupled cluster polarization propagator approximations (CCDPPA/CCSDPPA). We find that BH, CH+, and SiH+ are paramagnetic, MgH−, AlH, and GeH+ are diamagnetic and BeH− is a borderline case tilting towards paramagnetism. It is primarily variations in the diamagnetic contribution to the magnetizability that determine the overall sign of the magnetizability.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9220-9221 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using an operator identity, a sum-over-states expression for the diamagnetic contribution to the indirect nuclear spin–spin coupling constant is given. As the three other contributions also involve similar sum-over-states expressions, it thus becomes possible to apply the same method to the calculation of all contributions.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 7753-7760 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multipole solvent reaction field model is formulated within Møller–Plesset perturbation theory. The solvent is described as an isotropic dielectric medium characterized by a dielectric constant. Interactions between the solvent and the solute give rise to a modified Schrödinger-equation which is nonlinear with respect to the wave function. This leads to an iteration-scheme in order to obtain the solvent-modified correlation coefficients. Sample calculations are performed for a series of small neutral molecules and we compare the results with other correlated solvent methods. In the case of geometries no considerably changes are observed and the inclusion of electron correlation is crucial for describing the molecular properties of a solute. Total energies and energy-differences are very dependent on the dielectric medium. Furthermore, we outline future use of the model. © 2001 American Institute of Physics.
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