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Trygve Helgaker - One of the best experts on this subject based on the ideXlab platform.
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Nuclear Shielding constants by density functional theory with gauge including atomic orbitals
Journal of Chemical Physics, 2000Co-Authors: Trygve Helgaker, Philip J Wilson, Roger D. Amos, Nicholas C. HandyAbstract:Recently, we introduced a new density-functional theory (DFT) approach for the calculation of NMR Shielding constants.\nFirst, a hybrid DFT calculation (using 5% exact exchange) is performed on the molecule to determine Kohn-Sham orbitals and their energies;\nsecond, the constants are determined as in nonhybrid DFT theory, that is, the paramagnetic contribution to the constants is calculated from\na noniterative, uncoupled sum-over-states expression. The initial results suggested that this semiempirical DFT approach gives Shielding constants\nin good agreement with the best ab initio and experimental data; in this paper, we further validate this procedure, using London orbitals\nin the theory, having implemented DFT into the ab initio code DALTON. Calculations on a number of small and medium-sized molecules confirm\nthat our approach produces Shieldings in excellent agreement with experiment and the best ab initio results available, demonstrating its\npotential for the study of Shielding constants of large systems.
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Solvent effects on Nuclear Shieldings and spin–spin couplings of hydrogen selenide
The Journal of Chemical Physics, 1998Co-Authors: Per-olof Åstrand, Kenneth Ruud, Kurt V. Mikkelsen, Rgensen, Trygve HelgakerAbstract:Solvent effects on the Nuclear Shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the Nuclear Shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the Nuclear Shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as we...
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Magnetizability and Nuclear Shielding constants of solvated water
Chemical Physics Letters, 1996Co-Authors: Kurt V. Mikkelsen, Kenneth Ruud, Trygve HelgakerAbstract:We apply a recently developed model for calculating gauge origin independent molecular magnetic properties of solvated molecules to determine the magnetizability and Nuclear Shielding constants of solvated water. The solute is surrounded by a solvation shell and this supermolecule is enclosed in a spherical cavity immersed in a dielectric medium.
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Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution
The Journal of Physical Chemistry, 1996Co-Authors: Per-olof A, Kenneth Ruud, Kurt V. Mikkelsen, Trygve HelgakerAbstract:The effects of a dielectric medium on the magnetizabilities and Nuclear Shielding constants of the fluoromethanes are calculated in a gauge-origin independent approach. It is shown that in order to model the effects of a dielectric medium properly, we have to go beyond the dipole approximation and the geometry has to be optimized for each value of the dielectric constant. Geometrical distortions play an important role, as is clearly demonstrated for the magnetizability of the CH3F molecule where the geometrical distortions alter the sign of the dielectric contribution to the solvent shift. The effects on the Nuclear Shielding constants from a dielectric medium are interpreted in terms of the polarization of the charge distribution and the change in geometry. Other medium effects on Nuclear Shielding constants are discussed, and it is demonstrated that they must be included in order to reproduce the experimental gas-to-liquid chemical shift of the CH3F and CHF3 molecules. Basis set convergence and electron...
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MCSCF calculations of hypermagnetizabilities and Nuclear Shielding polarizabilities of CO and CH4
Molecular Physics, 1996Co-Authors: Sonia Coriani, Kenneth Ruud, Antonio Rizzo, Trygve HelgakerAbstract:The electric hypermagnetizabilities and Nuclear Shielding polarizabilities of the CO and CH4 molecules are computed using multiconfigurational linear response theory and a finite field method, in a mixed analytical-numerical approach. Extended sets of magnetic field dependent basis functions are employed. The use of the natural connection ensures good accuracy of the magnetic properties after numerical differentiation. The CO data are compared with other correlated literature results, and for CH4 the first correlated ab initio estimates of both properties are presented.
Kenneth Ruud - One of the best experts on this subject based on the ideXlab platform.
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Relativistic spin-orbit coupling effects on secondary isotope shifts of 13C Nuclear Shielding in CX2 (X = O, S, Se, Te)
Journal of the American Chemical Society, 2002Co-Authors: Perttu Lantto, Kenneth Ruud, Juha Vaara, Anu M. Kantola, Ville-veikko Telkki, Bernd Schimmelpfennig, Jukka JokisaariAbstract:Rovibrational corrections, temperature dependence, and secondary isotope shifts of the 13C Nuclear Shielding in CX2 (X = O, S, Se, Te) are calculated taking into account the relativistic spin−orbit (SO) interaction. The SO effect is considered for the first time for the secondary isotope shifts. The Nuclear Shielding hypersurface in terms of Nuclear displacements is calculated by using a density-functional theory method. Ab initio multiconfiguration self-consistent field calculations are done at the equilibrium geometry for comparison. 13C NMR measurements are carried out for CS2. The calculated results are compared with both present and earlier experimental data on CO2, CS2, and CSe2. The heavy-atom SO effects on the rovibrational corrections of 13C Shielding are shown to be significant. For CSe2 and CTe2, reliable prediction of secondary isotope effects and their temperature dependence requires the inclusion of the SO corrections. In particular, earlier discrepancies of theory and experiment for CSe2 ar...
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Solvent effects on Nuclear Shieldings and spin–spin couplings of hydrogen selenide
The Journal of Chemical Physics, 1998Co-Authors: Per-olof Åstrand, Kenneth Ruud, Kurt V. Mikkelsen, Rgensen, Trygve HelgakerAbstract:Solvent effects on the Nuclear Shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the Nuclear Shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the Nuclear Shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as we...
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Magnetizability and Nuclear Shielding constants of solvated water
Chemical Physics Letters, 1996Co-Authors: Kurt V. Mikkelsen, Kenneth Ruud, Trygve HelgakerAbstract:We apply a recently developed model for calculating gauge origin independent molecular magnetic properties of solvated molecules to determine the magnetizability and Nuclear Shielding constants of solvated water. The solute is surrounded by a solvation shell and this supermolecule is enclosed in a spherical cavity immersed in a dielectric medium.
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Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution
The Journal of Physical Chemistry, 1996Co-Authors: Per-olof A, Kenneth Ruud, Kurt V. Mikkelsen, Trygve HelgakerAbstract:The effects of a dielectric medium on the magnetizabilities and Nuclear Shielding constants of the fluoromethanes are calculated in a gauge-origin independent approach. It is shown that in order to model the effects of a dielectric medium properly, we have to go beyond the dipole approximation and the geometry has to be optimized for each value of the dielectric constant. Geometrical distortions play an important role, as is clearly demonstrated for the magnetizability of the CH3F molecule where the geometrical distortions alter the sign of the dielectric contribution to the solvent shift. The effects on the Nuclear Shielding constants from a dielectric medium are interpreted in terms of the polarization of the charge distribution and the change in geometry. Other medium effects on Nuclear Shielding constants are discussed, and it is demonstrated that they must be included in order to reproduce the experimental gas-to-liquid chemical shift of the CH3F and CHF3 molecules. Basis set convergence and electron...
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MCSCF calculations of hypermagnetizabilities and Nuclear Shielding polarizabilities of CO and CH4
Molecular Physics, 1996Co-Authors: Sonia Coriani, Kenneth Ruud, Antonio Rizzo, Trygve HelgakerAbstract:The electric hypermagnetizabilities and Nuclear Shielding polarizabilities of the CO and CH4 molecules are computed using multiconfigurational linear response theory and a finite field method, in a mixed analytical-numerical approach. Extended sets of magnetic field dependent basis functions are employed. The use of the natural connection ensures good accuracy of the magnetic properties after numerical differentiation. The CO data are compared with other correlated literature results, and for CH4 the first correlated ab initio estimates of both properties are presented.
Kurt V. Mikkelsen - One of the best experts on this subject based on the ideXlab platform.
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Solvent effects on Nuclear Shieldings and spin–spin couplings of hydrogen selenide
The Journal of Chemical Physics, 1998Co-Authors: Per-olof Åstrand, Kenneth Ruud, Kurt V. Mikkelsen, Rgensen, Trygve HelgakerAbstract:Solvent effects on the Nuclear Shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the Nuclear Shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the Nuclear Shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as we...
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Magnetizability and Nuclear Shielding constants of solvated water
Chemical Physics Letters, 1996Co-Authors: Kurt V. Mikkelsen, Kenneth Ruud, Trygve HelgakerAbstract:We apply a recently developed model for calculating gauge origin independent molecular magnetic properties of solvated molecules to determine the magnetizability and Nuclear Shielding constants of solvated water. The solute is surrounded by a solvation shell and this supermolecule is enclosed in a spherical cavity immersed in a dielectric medium.
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Calculation of Nuclear Shielding constants and magnetizabilities of the hydrogen fluoride molecule
The Journal of Chemical Physics, 1996Co-Authors: Per-olof Åstrand, Kurt V. MikkelsenAbstract:Nuclear Shielding constants and magnetizabilities of the hydrogen fluoride molecule have been calculated adopting the multiconfigurational self‐consistent field method. Effects of vibrational averaging are calculated by adopting a Gaussian function with variable width and position to describe the vibrational part of the wave function. The rovibrationally averaged 19F Shielding constant is calculated to 407.4 ppm and its anisotropy to 111.2 ppm, both in good agreement with experimental results. Also the isotope effect, 〈σF(DF)〉−〈σF(HF)〉, which is calculated to 3.0 ppm agrees well with the available NMR experiment. The effective geometry, dipole moment, vibrational frequencies, and rotational constants are also calculated and discussed.
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Magnetizabilities and Nuclear Shielding Constants of the Fluoromethanes in the Gas Phase and Solution
The Journal of Physical Chemistry, 1996Co-Authors: Per-olof A, Kenneth Ruud, Kurt V. Mikkelsen, Trygve HelgakerAbstract:The effects of a dielectric medium on the magnetizabilities and Nuclear Shielding constants of the fluoromethanes are calculated in a gauge-origin independent approach. It is shown that in order to model the effects of a dielectric medium properly, we have to go beyond the dipole approximation and the geometry has to be optimized for each value of the dielectric constant. Geometrical distortions play an important role, as is clearly demonstrated for the magnetizability of the CH3F molecule where the geometrical distortions alter the sign of the dielectric contribution to the solvent shift. The effects on the Nuclear Shielding constants from a dielectric medium are interpreted in terms of the polarization of the charge distribution and the change in geometry. Other medium effects on Nuclear Shielding constants are discussed, and it is demonstrated that they must be included in order to reproduce the experimental gas-to-liquid chemical shift of the CH3F and CHF3 molecules. Basis set convergence and electron...
Per-olof Åstrand - One of the best experts on this subject based on the ideXlab platform.
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Solvent effects on Nuclear Shieldings and spin–spin couplings of hydrogen selenide
The Journal of Chemical Physics, 1998Co-Authors: Per-olof Åstrand, Kenneth Ruud, Kurt V. Mikkelsen, Rgensen, Trygve HelgakerAbstract:Solvent effects on the Nuclear Shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the Nuclear Shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the Nuclear Shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as we...
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Calculation of Nuclear Shielding constants and magnetizabilities of the hydrogen fluoride molecule
The Journal of Chemical Physics, 1996Co-Authors: Per-olof Åstrand, Kurt V. MikkelsenAbstract:Nuclear Shielding constants and magnetizabilities of the hydrogen fluoride molecule have been calculated adopting the multiconfigurational self‐consistent field method. Effects of vibrational averaging are calculated by adopting a Gaussian function with variable width and position to describe the vibrational part of the wave function. The rovibrationally averaged 19F Shielding constant is calculated to 407.4 ppm and its anisotropy to 111.2 ppm, both in good agreement with experimental results. Also the isotope effect, 〈σF(DF)〉−〈σF(HF)〉, which is calculated to 3.0 ppm agrees well with the available NMR experiment. The effective geometry, dipole moment, vibrational frequencies, and rotational constants are also calculated and discussed.
Rgensen - One of the best experts on this subject based on the ideXlab platform.
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Solvent effects on Nuclear Shieldings and spin–spin couplings of hydrogen selenide
The Journal of Chemical Physics, 1998Co-Authors: Per-olof Åstrand, Kenneth Ruud, Kurt V. Mikkelsen, Rgensen, Trygve HelgakerAbstract:Solvent effects on the Nuclear Shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the Nuclear Shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the Nuclear Shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as we...
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Electric field dependence of magnetic properties: Multiconfigurational self‐consistent field calculations of hypermagnetizabilities and Nuclear Shielding polarizabilities of N2, C2H2, HCN, and H2O
The Journal of Chemical Physics, 1995Co-Authors: Antonio Rizzo, Trygve Helgaker, Kenneth Ruud, Andrzej Barszczewicz, Michal, Jaszuński, RgensenAbstract:Multiconfigurational self‐consistent field (MCSCF) response is used to study the electric field dependence of magnetizabilities and Nuclear Shielding constants for N2, C2H2, HCN, and H2O. London perturbation‐dependent atomic orbitals are used to ensure gauge origin independence. The computed magnetizabilities and Shielding derivatives show a strong electron correlation dependence. The N2 results confirm the conclusions of previous ab initio studies. For the other molecules, this is the first study of the above magnetic properties beyond the SCF approximation.
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Multiconfigurational self-consistent field calculations of Nuclear Shieldings using London atomic orbitals
The Journal of Chemical Physics, 1994Co-Authors: Kenneth Ruud, Trygve Helgaker, Rgensen, Rika Kobayashi, Keld L. Bak, Rgen Aa. JensenAbstract:Nuclear Shielding calculations are presented for multiconfigurational self‐consistent field wave functions using London atomic orbitals (gauge invariant atomic orbitals). Calculations of Nuclear Shieldings for eight molecules (H2O, H2S, CH4, N2, CO, HF, F2, and SO2) are presented and compared to corresponding individual gauges for localized orbitals (IGLO) results. The London results show better basis set convergence than IGLO, especially for heavier atoms. It is shown that the choice of active space is crucial for determination of accurate Nuclear Shielding constants.
