Molecular polarizability in quantum defect theory: Non-polar molecules

The Green function in the quantum defect theory provides an exact account for the high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wavefunctions calculated ab initio. As an application we present simple and efficient semi-analytical method for calculation of dynamic polarizabilities of nonpolar molecules. The method is applied to alkali dimers Li₂, Na₂ and Rb₂. The result of benchmark calculation (H₂ molecule) are in good agreement with experimental data; the accuracy achieved is comparable with that of ab initio calculations. We also calculate Verdet constants of the above molecules in Becquerel approximation.