Fano-Feshbach formalism applied to the calculation of autoionization widths through analytic continuation

A method to calculate the autoionization width from a discretized pseudo-spectrum is proposed. This method relies on an analytic continuation of Green's function within the Fano-Feshbach formalism. The pseudo-spectrum is obtained at the multireference configuration interaction level in a square-integrable basis set, commonly found in quantum chemistry software. Few states around the desired resonance are needed to perform the analytic continuation. This method was applied to atomic (He and Ne) and molecular (HF and benzene) systems, and the results for the autoionization width show good agreement with the available theoretical and experimental values.