On the importance of scale and polarization of the atomic orbital basis for LCAO calculations of electronic intensities

Abstract

The importance of scale and polarization of the atomic basis set for LCAO calculations of the intensities of electronic transitions is investigated using the molecular hydrogen ion, H 2 + , as a model. The transitions under consideration are the 1σ g−1σ u the 1π u−1π g and the 1σ g−1πuit excitations of this ion, and the electric dipole transition moments are calculated for a range of nuclear separations using the dipole length, the dipole velocity, the dipole acceleration and the time-derivative of the dipole acceleration formulations. For the 1σ g−1σ u and the 1π u−1π g excitations scaling and/or polarization are found very efficient for the improvement of the calculated transition moments for small internuclear separations for all the dipole formulations, whereas only the dipole length and the dipole velocity results are well-behaved for large separations. For the 1σ g−1π u excitation scaling is found to be more important than polarization for all internuclear separations.