Basis-set effects on calculated molecular magnetic properties

Abstract

The magnetic susceptibility of the BH molecule and the screening constants of its nuclei have been calculated by the finite perturbation SCF method, using London field-dependent atomic orbitals. Several sets of contracted Gaussian functions have been used. The split valence triple-zeta basis set augmented with bond functions and lone-pair functions gave good results with regard to accuracy and computer time. The calculated quantities are close to those obtained by other authors using very large field-independent basis sets.

Calculation of 13C‐NMR chemical shift using the intermediate neglect of differential overlap model

“…The ability to present a balanced treatment of transition moments in a finite basis, as with excitation spectra [55,56], does not imply adherence to the orbital completeness relations [Eq. (12)] that were involved in this study. The localization methods do, however, dampen the effect of remote contributions to shielding even for the small basis utilized.…”

“…Many empirical and semiempirical models have been developed to predict specific chemical shifts in terms of the chemical properties of the atoms of interest and the specific bonding environment [4-111. These models and rules are very useful in interpreting the nature of the local chemical environment in a molecule. Direct nonempirical calculations of chemical shift have met with only modest success and normally require very large basis sets to obtain quantitative accuracy [12,13]. The failure of smaller basis sets is usually attributed to their inability to represent the gauge invariance of the origin of the externally applied field [14,15].…”