An object of central importance in quantum chemistry is the electron density ρ(r) : R 3 → R + . Bader demonstrated a correspondence between the basins of attraction of the electron charge density and atoms in molecules . Specifically, each basin of attraction contains exactly one atom in a molecular system, allowing one to uniquely assign the electronic charge present on each atom as the integral of the charge density over its basin of attraction. This leads to the bader charges, here defined in R 3 as