where {r i } and {w i } are a set of quadrature points and weights, respectively. For molecular integrals, it makes sense to partition the sum in eq. A1 into atomic regions and to use nuclear-centered grids for each region. The partition is accomplished using Voronoi polyhedra, 138 defined by the nuclei. The idea is to define a weight function w A (r) for each atom A, such that the normalization condition A w A (r) = 1 (A2) holds at every point r in three-dimensional space. This condition implies that the integrand in eq. (A1) can be decomposed into atomic contributions,