G. Hummer, ELECTROSTATIC POTENTIAL OF A HOMOGENEOUSLY CHARGED SQUARE AND CUBE IN2 AND 3 DIMENSIONS, Journal of electrostatics, 36(3), 1996, pp. 285-291
A closed form of the electrostatic potential of a homogeneously charge
d cube is derived by integration. The exact result is compared with mu
ltipole expansions for the exterior and interior of the cube. The elec
trostatic potential of a homogeneously charged square in two-dimension
al electrostatics is also determined.