Ab initio Hartree–Fock calculation of the elastic electron scattering cross section of sulphur hexafluoride

Abstract

The ab initio Hartree–Fock calculation of the elastic electron scattering cross section of sulphur hexafluoride is reported. The integrals for the Born scattering amplitudes have been evaluated by a new simple technique, based on Gaussian quadrature. Spherical averaging was performed numerically; different techniques for spherical averaging are discussed. An estimated re structure was used and vibrational effects have been neglected. In order to assess the effect of the basis set on the intensities, calculations have been performed for the nitrogen molecule with six different basis sets. Using these results as a guide, a triple-zeta basis set, augmented with polarization functions and diffuse functions, was selected for SF6. The results confirm Bartell’s hypothesis that the observed residuals from the independent atom model intensities are due to electronic bonding effects. It is suggested that, for very accurate electron diffraction work, the effect of electron redistribution has to be taken into account by ab initio calculations.