Hellmann potential in the J-matrix approach: I. Eigenvalues

The trajectories of the poles of the S-matrix for Hellmann potential, in the complex energy plane, have been studied near the critical screening parameter. The calculation has been performed using the J-matrix approach, which uses a suitable L2 basis to tridiagonalize the reference Hamiltonian matrix. The calculated bound and resonance state energies have been compared with available numerical data.