1,721,131 research outputs found
ERRATUM: Theory of nuclear electric shielding in molecules
No full textSee Also: Original: P. Lazzeretti and R. Zanasi, Theory of nuclear electric shielding in molecules, Phys. Rev. A 24, 1696 (1981
Theoretical determination of the magnetic properties of HCl, H_2S, PH_3, and SiH_4 molecules
No full textCoupled Hartree–Fock perturbation theory has been applied to evaluate second-order magnetic properties of HCl, H2S, PH3, and SiH4 molecules. An efficient procedure for processing only symmetry distinct two-electron integrals in the coupled HF algorithm is outlined, which permits the use of very large basis sets of expansion with limited computer efforts. Several near Hartree–Fock wave functions are examined, particular attention being devoted to the role of polarization functions for the second-row atoms. Comparison between computed and available experimental results is gratifying and demonstrates the practicability of perturbed HF calculations based on the group-theoretical procedure sketched in this paper. An analysis of the gauge dependence affecting the calculated values is performed, which yields a severe test on the reliability of the present calculations
Calculation of vertical ionization potentials of CF_4 and SiF_4 by the Green-Function method
No full textA Green-function method is employed,within the framework of the CNDO approximation to the zero-order wavefunction, to calculate the photoelectron spectrum of the CF4 and SiF4 molecules. The agreement between theoretical and experimental ionization potentials is quite good and a sensible improvement with respect to Koopmans' approximation is obtained. Two different expansion for the self-energy are discussed
Analytical dipole moment geometrical derivatives from nuclear electric shielding in molecules
No full textWe present ab initio calculations of dipole moment geometric derivatives for some first-row atom hydrides. Dipole moment derivatives, in terms of atomic polar tensors (APT), are equivalent to nuclear electric shieldings and were determined analytically, within the random phase approximation (RPA). Polarized basis sets were used, which give accurate results with small computer effort
The validity of the Musher's model for the magnetic properties of aromatic molecules.
No full textPlots of proton magnetic shielding density in the benzene molecule, obtained via accurate coupled Hartree-Fock calculations, are reported. They unequivocally show that proton deshielding is due to local effects arising in the adjacent carbon atom and C--- H bond. Therefore downfield chemical shifts observed in proton magnetic resonance spectroscopy can be entirely explained in terms of magnetic anisotropy of the carbon environment. This shows the unphysical character of the ring current model and the reliability of Musher's model
Connection between the nuclear electric shielding tensor and the infrared intensity
No full textThe integrated IR intensity can be directly related to the electric shielding tensor of the nuclei in a molecule. This allows us to measure, by IR spectroscopy, the effective electric field at the nuclei of a molecule immersed in an external electric field. Relations exist with the dynamic polarizability and the magnetizability, which implies the possibility of a unified treatment of electric and magnetic second-order properties
Ab initio study of a 32-boron cluster: B_32H_32^{2-}
No full textResponse properties of B_32H_32^{2-} are theoretically estimated
Response tensors for chiral discrimination in NMR spectroscopy
No full textResponse tensors that may be used forrationalising chiral discrimination by nuclear magneticresonance spectroscopy are selected relying on the criterionthat the induced molecular electric moment andthe induced magnetic field at a nucleus are invariant toa translation of the coordinate system
Bond Length Dependence of First Hyperpolarizabilities in HF and HCl Molecules
No full textCoupled Hartree-Fock perturbation theory is applied in extended ab initio calculations of molecular dipole moments, polarisabilities and first hyperpolarisabilities of first-row hydrides. Their dependence on internuclear separation is also analysed and discussed. Very strong hyperpolarisability gradients and large vibrational corrections are found. The relevance of the present results for interpreting the discrepancies between experimental and theoretical hyperpolarisabilities is pointed out
Singularities of Magnetic-Field Induced Electronic Current Density: A Study of the Ethylene Molecule
No full textThe singularities of the quantum-mechanical electron current density induced in a molecule by an external magnetic field are analyzed via the theory of the real autonomous systems of differential equations. Group-theoretical techniques, based on the idea of color symmetry, are developed, which predict the occurrence of singularities about molecular symmetry elements. Plots of induced electron current density have been obtained for the ethylene molecule through accurate coupled SCF calculations. The theoretical magnetic properties of ethylene obtained through this investigation are the most accurate reported so far
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