Extraction of Stewart atoms from electron densities

Stewart atoms are the unique nuclear-centered spherical functions whose sum best fits a molecular electron density in a least-squares sense. It is difficult, however, to express Stewart atoms in closed form. We therefore introduce new closed-form approximations, Stewart-Slater atoms, and show that these can be found efficiently from molecular multipole moments. Using examples, we argue that the parameters of Stewart-Slater atoms can yield insight into the nature of chemical bonding.