The negative ion charge density around a negatively charged sphere inside a silica cylindrical cavity. The ionic strength is 0.015M. There are 473 charges on the cylinder and 16 on the sphere. Three dimensional periodic boundary conditions were employed. This is a model for dendrimer separation in size exclusion chromatography. The charge density is obtained from numerical solution of the nonlinear Poisson-Boltzmann equation using multigrid techniques. The free energy profile can be computed once the PB equation is solved for a series of sphere locations.

A contour plot of the same charge density.

The positive ion charge density around a negatively charged dendrimer sphere.