Dynamic Polarizabilities of Diatomic Molecules: A Comparison of the ab initio and Density Functional Theory Methods with the Reduced-Added Green Function Method of the Quantum Defect Theory

The quantum defect theory is used to test the accuracy of the ab initio and density functional theory (DFT) methods in calculations of the dynamic polarizabilities of diatomic molecules. Our testing is restricted only to those variants of these methods which are most accurate in calculations of static polarizabilities. The testing results show that one of the main errors of the ab initio and DFT methods is related to inaccuracies in determining the energies of excited states, where dynamic polarizabilities have resonant maxima.