Dirac eigenvalues for a softcore Coulomb potential in d dimensions
  A single fermion is bound by a softcore central Coulomb potential V(r) = -v/(r^q + b^q)^(1/q), v>0, b>0, q \ge 1, in d>1 spatial dimensions. Envelope theory is used to construct analytic lower bounds for the discrete Dirac energy spectrum. The results are compared to accurate eigenvalues obtained numerically. 
Richard L. Hall and Petr Zorin
math-ph math.MP physics.atom-ph