This is an exercise for advanced students. The exercise will demonstrate that the corrector-predictor approach for solving the Poisson equation can be very troublesome. Thus the standard numerical solution to the Poisson equation is the preferred approach.
Researchers should cite this work as follows:
Dragica Vasileska; Gerhard Klimeck (2008), "PN Diode Exercise: Graded Junction," http://nanohub.org/resources/4898.