The method of reduced-added Green's function in quantum defect approximation ͓V. E. Chernov, D. L. Dorofeev, I. Yu. Kretinin, and B. A. Zon, Phys. Rev. A 71, 022505 ͑2005͔͒ is generalized for calculation of dynamic polarizabilities of nonpolar molecules. The method is applied to alkali-metal dimers Li 2 , Na 2 , and Rb 2 . The accuracy achieved in benchmark calculation ͑H 2 molecule͒ is comparable to that of ab initio calculations. 1 It was considered for a long time that QDT description is successful only for one electron over complete shells, e.g., for alkalimetal-like atoms and ions. After an error in earlier QDT has been corrected in Ref. ͓14͔, the modified QDT is capable to treat optical electron states in any complex atom. The wave function of such a state is determined by the QDs of the whole spectral series ͑not only by the QD of the given state͒.

The reduced-added Green's function technique in the quantum defect theory combines the advantages of analytical and ab initio methods in calculating frequency-dependent (dynamic) polarizabilities of atoms and molecules, providing an exact account for the high-excited and continuum electronic states. In the present paper this technique is modified to take into account the long-range dipole potential of a polar molecule core. The method developed is applied to calculation of the dynamic polarizability tensors of alkali-metal hydrides LiH and NaH as well as to some fluorides (CaF and BF) in the frequency range up to the first resonances. The results are in good agreement with ab initio calculations available for some frequencies.

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.

Synopsis The reduced-added Green's function technique in quantum defect approximation is generalized for calculation of dynamic polarizabilities of molecules. The method is applied to alkali metal hydrides and dimers as well to sime other simple molecules. The accuracy achieved in benchmark calculations for H2 molecule is comparable with that of the ab initio methods.

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