Green's function for the Dirac equation with nonsingular central potential and complex energy. Estimation algorithm

Calculation of the electron radial Green's function leads to solution of a system of ordinary differential equations for three functions: F, G, which represent the regular solution of the Dirac equation for r → 0, and W− (the antiWronskian) —a function regular everywhere: W− = 1 for r = 0; W− ≈ 1/r as r →∞. An algorithm is formulated for calculating boundary values of W− as r → 0 and for estimation purposes at asymptotically large values of r.