public void method setupGrid sets up a grid around the solute particles
using the center of geometry as the grid center, along with the given
gridspacing, ionic strength, solute/solven permittivities and the number of gridpoints along X,Y and Z.
public boolean solveforpotential solves the linearized Poisson-Boltzmann equation
for the electrostatic potential phigrid using the incomplete cholesky conjugate gradient algorithm