If the potential is attractive, the trajectories will bend toward one another on each side of the potential center, causing a breakdown in both (1) and . Maxwell solved a similar equation breakdown by adding a term; we should do the same. The derivative in (1) causes the singularity, so try subtracting ∇ 2 i R (linear in R, otherwise we get another nonlinearlty; subtract to cancel). We must however enforce density relativity by dividing by R: -∇ 2 i R/R. To make sure this cancels the problem in the derivative, generalize to