Eigenchannel Theory and R-Matrix Theory

We here combine the eigenchannel theory and R-matrix theory to calculate the eigenchannel parameters of multichannel quantum defect theory directly. There are two advantages: (1) an analytical unified treatment of perturbed discrete Rydberg states, autoionizing states and their adjacent continuum to avoid numerical calculations, outside the R-matrix box; (2) clear assignment of overlapped resonances.