Close-coupling calculation for the 2Σu+ state of H2-

We demonstrate the utility of the close-coupling approximation, usually applied to scattering problems, for calculations of molecular bound states. Our primary test case is the 2Σu+ state of H2-. While limited to Hartree-Fock accuracy, our analysis of this resonant state within the bound region parallels closely the results from more precise quantum-chemical calculations. Specifically, the crossing between the neutral and negative-ion curves occurs at an internuclear separation of 3.025 a.u. in our calculation, in good agreement with a multireference configuration-interaction approach of previous authors. The shape and total energy of the anion curve, when corrected for by the correlation energy of the target at the crossing, is also in good agreement with earlier results. The method is then extended into the unbound or resonant-state region by studying the shape-resonance behavior of scattering eigenphase sums