The Coulomb interaction between two protons is a special problem, in that its expansion in separable potentials does not converge, but this is handled by matching the Faddeev solutions to long range coulomb solutions, instead of to plane waves.
Maxwell's Equations | Maxwell's equations | London equations | Faddeev–Popov ghost | power series solution of differential equations | Navier–Stokes equations | Maxwell's equations in curved spacetime | Ludvig Faddeev | Kirsch equations | Equations of motion | Einstein's equations | Einstein field equations |