The quadrupole polarizability and spectral moments of the quadrupole oscillator strength distribution of N₂

Abstract

We report the spectral moments for 0 ˇ- k ˇ- -6 of the quadrupole oscillator strength distribution (QOSD) of N₂ as calculated in the polarization propagator formalism. The moments with k ˇ- -3 have not been calculated before. The choice of basis and of inclusion of correlation to the level of RPA are discussed. The accuracy of the calculated QOSD's is estimated from sum rules, completeness relations and origin dependence. We conclude that f-orbitals are an essential ingredient for the basis, and that correlation must be included in a balanced way. Vibrationally averaged spectral moments are reported. We calculate the quadrupole polarizability and its components, and find α₂ = 76·54 a.u. (Hartree atomic units), in good agreement with other calculations.