The use of PEqS requires a dense three-dimensional grid with ε(r) defined at every point. For the model environments considered here, where the dielectric constant is defined atomwise, this requires smooth interpolation between different atomic values of the dielectric constant (ε A in eq. 28). values of ε. For this we use Becke's version of Voronoi cells with smooth boundaries. This scheme was developed by Becke for numerical evaluation of three-dimensional integrals,