Spectral bounds for the cutoff Coulomb potential
  The method of potential envelopes is used to analyse the bound-state spectrum of the Schroedinger Hamiltonian H = -Delta -v/(r+b), where v and b are positive. We established simple formulas yielding upper and lower energy bounds for all the energy eigenvalues. 
Richard L. Hall and Qutaibeh D. Katatbeh