Accurate width and position of lowest 1S resonance in H− calculated from real-valued stabilization graphs

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Abstract
The use of real‐valued stabilization graphs for calculation of resonance energies and widths is considered in connection with the lowest Feshbach resonance state of H−, nominally (Φ2s)2. One problem that arises is the difficulty of generating stabilization graphs with well defined avoided crossings between the resonance state of interest and nearby interacting continuum states. For this purpose, criteria are developed for selection of basis sets and CI lists and for determination of suitable stabilization parameters. Another problem is the extraction of resonance parameters from the stabilization graph. We study one particular analytic continuation procedure recently proposed by Isaacson and Truhlar. Criteria for separation of physical from nonphysical solutions of the complex energy stationary point, for determination of the necessary numerical precision for the input real eigenvalues, and for other details of the method have all been examined. The results for H−, even with a modest Gaussian basis set and partial CI list, are in excellent agreement both with experiment and with more elaborate calculations by other methods. It is concluded that the method is capable of describing electronic resonances to high accuracy and shows promise for application to systems more complicated than H−.