Algorithm for locating narrow resonances in coupled-channel quantal scattering calculations

We present a definition for the absolute eigenphase sum for multichannel quantum-mechanical scattering problems. The absolute eigenphase sum is useful for finding resonance, especially very narrow and hard-to-locate ones, for which the savings in computer time can be very large. We have demonstrated the practicality of the method by implementing it to locate a resonance in the diabatic representation with the Numerov method and in the adiabatic representation with R-matrix propagation.