In order to to numerically solve Poisson's equation (Equation
#eqnpoisson#113>), it is necessary to notice that its steady state
solution is the same as that for diffusion, and can be solved by
iteration of the 3D successive over-relaxation equation for a field
without free charge:
#equation114#
Where #tex2html_wrap_inline1290# is a relaxation rate not to exceed 2, and is best
determined empirically.