Abstract
The regularized method of analytic continuation is used to study the low-energy negative-ion states of beryllium (configuration 2s(2)epsilon p P-2) and magnesium (configuration 3s(2)epsilon p P-2) atoms. The method applies an additional perturbation potential and requires only routine bound-state multi-electron quantum calculations.
Such computations are accessible by most of the free or commercial quantum chemistry software available for atoms and molecules. The perturbation potential is implemented as a spherical Gaussian function with a fixed width.
Stability of the analytic continuation technique with respect to the width and with respect to the input range of electron affinities is studied in detail. The computed resonance parameters E-r = 0.282 eV, Gamma = 0.316 eV for the 2p state of Be- and E-r = 0.188 eV, Gamma = 0.167 for the 3p state of Mg- agree well with the best results obtained by much more elaborate and computationally demanding present-day methods.