G.P. Arrighini

Magnetic Properties of Polyatomic Molecules. II. Proton Magnetic Shielding Constants in H2O, NH3, CH4, and CH3F

Proton magnetic shielding constants in H2O, NH3, CH4, and CH3F molecules have been evaluated by the perturbed HF scheme, by employing extended basis sets of Slater orbitals. Explicit formulas for both diamagnetic and paramagnetic contributions to the observable are given, for a gauge transformation corresponding to any change of the origin of the external vector potential. The calculated results are in fairly good agreement with the experimental data, when the chosen gauge is coincident with the central nucleus of the molecule.

SCF‐MO's and Molecular Properties of Methane

SCF‐MOs of the CH4 molecule have been calculated for the experimental geometry by using bases of up to 39 STOs. The best molecular energy obtained is −40.20452 a.u. The ground‐state wavefunctions have been utilized to compute some one‐electron properties, viz., the electric octupole moment, the electric field gradient at the protons, and the diamagnetic susceptibility. In addition, the electric polarizability and the paramagnetic susceptibility have been evaluated using a perturbed H–F calculation.

SCF MO's and Molecular Properties of H2O

SCF MOs of H2O molecule have been calculated for a geometry very close to the experimental one, using a basis set of 29 STOs. The evaluated HF energy is −76.0384 a.u. Several ground‐state one‐electron properties have also been computed, viz., the first three electric multipole moments, electric field and gradient field at the nuclei, electric polarizability, and magnetic susceptibility.

Electric polarizability of polyatomic molecules

Abstract Electric polarizabilities of some polyatomic molecules are evaluated, within the HF pertubative scheme, by using LCAO SCF MOs wave functions.

Magnetic properties of polyatomic molecules. III. Magnetic shielding constants of heavy nuclei in H217O, 14NH3, 13CH4 and 13CH3F☆

Abstract The nuclear magnetic shielding tensor components for 17 O in H 2 17 O. 14 N in 14 NH 3 and 13 C in both 13 CH 4 and 13 CH 3 F have been evaluated by coupled HF perturbation theory. All quantities needed to calculate the tensor components for any gauge are also reported. The gauge-invariance of the computed quantities is not uniformly good for the various examples investigated.

Electric and magnetic properties of N2 and H2O by the equations‐of‐motion method

Dynamic multipole polarizabilities and the magnetic dipole susceptibility of N2 and H2O are evaluated in the framework of the equation‐of‐motion method corresponding to the random phase (RPA) and Tamm–Dancoff approximations (TDA). The results are presented in the form of a Cauchy expansion truncated after the ω4 terms. Nuclear magnetic shielding constants of N, H, and O are obtained as by products of the main calculations. While the RPA results for the magnetic properties compare very well with available experimental data, the computed values for the electric observables are only in moderately good agreement with the experiments, suggesting an inadequacy of the employed basis sets and a different relevance of the correlation effects as well. The dipole–dipole van der Waals dispersion coefficients for the pairs N2–N2, H2O–H2O, and N2–H2O obtained by RPA values of the dipole polarizability at imaginary arguments compare only approximately well with semiempirical estimates.

More on the quantum propagator of a particle in a linear potential

The construction of the exact quantum propagator of a particle subjected to a constant force offers a challenge to existing propagator methodology. Here, besides considering the traditional approach, which involves an expansion in the complete set of energy eigenstates, we illustrate (i) the merits of a rather more elegant procedure founded on the ‘‘disentanglement’’ of the time‐evolution operator and (ii) the power of a general treatment based on a time‐dependent variational approach.

SCF MO's and Molecular Properties of Methyl Fluoride

The SCF MOs of CH3F have been calculated by using bases of up to 47 STOs. The best molecular energy obtained is − 139.0612 a.u. The ground‐state wavefunctions have been utilized to compute several observables corresponding to one‐electron operators, viz., the electric dipole, quadrupole, and octopole moments, the electric field gradient at the carbon atom and at the proton, and the diamagnetic part of the susceptibility. In addition, by using the coupled HF perturbation theory, the electric polarizability and the paramagnetic part of the susceptibility have been computed.

Long-range interaction energy of two- and four-electron atoms☆

Abstract The first three long-range dispersion coefficients C 6 , C 8 and C 10 for all the pairs of atoms which arise from the iso- electronic sequences HeC 4+ , BeC 2+ have been obtained by coupled time-dependent Hartree—Fock theory. In addi- tion, some comparisons with other more approximate schemes contained in that method have been carried out

Inelastic scattering of fast electrons from molecular systems. I. Hydrogen molecule

Abstract Inelastic scattering of fast electron from the electronic ground state of the H 2 molecule is investigated within the first Born approximation. The relevant transition properties have been obtained in some approximation corresponding so ??? order solutions of the equations-of-motion formation put forward by Rowe-Tamm-???approximation, random phase approximation. Generalized oscillator strengths and ??? of different symmetry are evaluated and discussed.