Frequency-dependent polarizabilities of diatomic molecules: ab initio methods and density functional theory compared with quantum-defect reduced-added Green function technique

The quantum defect theory is used to test the accuracy of ab initio methods and density functional theory (DFT) in calculating the frequency-dependent polarizabilities of diatomic molecules. We confine ourselves to testing only those variants of these methods that are most accurate for calculating static polarizabilities. The test results show that one of the main errors of the ab initio and DFT methods is associated with inaccuracies in determining the energies of excited states, where frequency-dependent polarizabilities have resonance maxima.