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An application of the continuous transformation of the origin of the current density (CTOCD) scheme to constrain the diamagnetic induced charge current density (Jd) to be divergenceless is introduced. This results in a family of Jd fields perpendicular and proportional to both the gradient of the electron density and the external magnetic field. Since, in the limit of a complete basis set calculation, the paramagnetic component Jp also becomes divergenceless, we call this scheme CTOCD-DC (CTOCD for Divergenceless Components). CTOCD-DC allows for a topological characterization of both Jd and Jp in terms of their stagnation graphs. All stagnation graphs of Jd from CTOCD-DC contain the zero points of the gradient of the unperturbed electron density (∇ ρ). In this way, an intimate topological relation between ρ and the diamagnetic current contribution is revealed. Numerical experiments exemplified by the case of LiNHF in point group symmetry C1 suggest that the corresponding paramagnetic current contributions Jp can show tendencies to accumulate pseudo-stagnation lines in proximity of some kind of the zero points of ∇ ρ. Common zero points of ∇ ρ and the total currents are exactly zero points of the mechanical momentum density. [ABSTRACT FROM AUTHOR]

A new method for the calculation of molecular magnetic susceptibility and nuclear magnetic shielding is presented. It is based on continuous transformations of origin of the current density which make the transverse part of the paramagnetic current vanish. For any molecule all the components of the nuclear magnetic shielding tensor provided by the new method are independent on the origin of the gauge, whereas the components of the magnetizability tensor are translationally invariant only for center-symmetric molecules (they, in general, show a linear dependence on the shift of origin). This method, termed CTOCD-PZ, has been implemented for the theoretical determination of molecular magnetic properties via numerical integration techniques and, from preliminar results obtained for methane and carbon dioxide molecules, reveals reliable. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The results of an accurate calculation of second-order properties of the ammonia molecule are reported, with particular attention to nuclear electromagnetic shielding tensors. These quantities enable one to evaluate the actual fields at the nuclei of a molecule perturbed by external radiation. The present theoretical study provides an extended numerical test on the mutual relationships among different properties. A theoretical scheme, based on force and torque gauges for the transition moments, has been applied to partition the molecular polarizabilities, the paramagnetic susceptibilities, and other properties into atomic terms transferable from molecule to molecule. [ABSTRACT FROM AUTHOR]

Polarized basis sets are used to compute dipole and quadrupole derivatives of the hydrides LiH, CH4, NH3, H2O, and HF. Analytic calculation of derivatives is compared with calculation via the dipole and quadrupole electric shielding tensors. With these basis sets, violation of the Hellmann–Feynman theorem is only about 0.01 a.u. in dipole derivatives and 0.02 a.u. in quadrupole derivatives. [ABSTRACT FROM AUTHOR]

The results of an accurate calculation of second-order properties of the methane molecule are reported, with particular emphasis on dynamic shielding tensors, which enable one to evaluate the effective fields acting on the nuclei of a molecule in the presence of an electromagnetic field. The present theoretical study provides an extended numerical test, showing the reciprocal relations among different properties, i.e., sum rules and formulas explicitly linking molecular response tensors. A scheme for partitioning molecular properties into atomic contributions is discussed, which seems to imply transferability of average electric dipole polarizabilities. [ABSTRACT FROM AUTHOR]

We 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. [ABSTRACT FROM AUTHOR]

The connection between the nuclear electric shielding and the atomic polar tensors are shown. The electric shielding tensors are related to the polarizability and the magnetizability, and satisfy a constraint condition for the electrostatic equilibrium which is the mixed length-acceleration Thomas–Reiche–Kuhn sum rule. In addition, they can be successfully used to rationalize experimental IR intensity data, which is verified by extended basis set calculations on the water molecule. [ABSTRACT FROM AUTHOR]

General constraints for invariance of magnetic properties in a gauge transformation are analyzed. Sum rules relative to the transformation from Coulomb to Landau gauges are examined in particular. Numerical tests for hydrogen fluoride, water, ammonia, and methane molecule have been carried out in large basis set calculations, using random-phase approximation. The conditions for invariance are severe conditions for accuracy of variational molecular wave functions. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Theoretical methods based on the random-phase approximation have been applied to evaluate near Hartree–Fock dynamic electric polarizability and shielding tensors of carbon and hydrogen nuclei in the benzene molecule. Cauchy moments of the various properties have been determined. The results obtained in different gauges (dipole length, velocity, and acceleration) are reported. [ABSTRACT FROM AUTHOR]

The magnetic susceptibility and the nuclear magnetic shielding tensors of HF, NH3, and CH4 molecules in the presence of a spatially uniform time-independent magnetic field have been calculated within the Landau gauge for the vector potential. The random-phase approximation has been used, adopting flexible Gaussian basis sets of large size. Magnetic susceptibilities are quite harder to evaluate accurately in the Landau gauge than in Coulomb gauge. Calculated nuclear magnetic shieldings are close to the Hartree–Fock limit. Sum rules for charge conservation and origin independence of magnetic susceptibility and nuclear magnetic shieldings are fairly well satisfied by basis sets of extended size. [ABSTRACT FROM AUTHOR]

It was recently shown that vibrational rotational strengths of chiral molecules can be expressed in terms of two nuclear shielding tensors, γλαβ(0) and ξλαβ(0). We report the first calculations of vibrational rotational strengths from these nuclear shielding tensors. The molecule studied is NHDT. Calculations are carried out at the SCF level using the random phase approximation. γλαβ(0) is calculated using length, momentum and force representations. ξλαβ(0) is calculated using angular momentum and torque representations. A range of basis sets, both ‘‘conventional’’ and ‘‘polarized’’ in type, are employed. Gauge and origin dependence are also investigated. [ABSTRACT FROM AUTHOR]