Properties of doubly-excited states of Li-and Be: the study of electron correlations in hyperspherical coordinates

Abstract

By adopting a frozen-core approximation with the two valence electrons treated in suitably chosen model potentials, the correlations of doubly-excited states of Li- and Be are studied in hyperspherical coordinates in the adiabatic approximation. The characteristics of correlation patterns for these states are found to be similar to those for the corresponding states of H- and He except for the gradual loss of the strong angular correlation for Li- and Be at large hyper-radius. Adiabatic potential curves and eigenenergies for the doubly-excited states lying below the n=2 and n=3 limits of the one-electron ions are calculated and compared with results from the configuration interaction method using the same model potential to assess the validity of the adiabatic approximation. It is concluded that for certain (L, S, pi ) states the adiabatic approximation is quite adequate but for others, e.g. 1P0, couplings between neighbouring channels are important.