Pseudoatoms of the electron density

The theory of molecular structure, developed by Bader and co-workers, has met with considerable success and is now being applied to many aspects of chemistry. One finding, however, that has complicated the theory is that of non-nuclear attractors, that is, pseudoatoms. In this study we examine basis set and to some extent electron correlation effects on the appearance and disappearance of non-nuclear attractors in Li2, Na2, Na4, and Na5. The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of −∇2ρ(r) for the valence shell of the atom. This and the fact that the pseudoatom is also present in the promolecule indicates that the pseudoatoms are remnants of or, in fact, are portions of atoms that are not perturbed enough in the molecule to remove an essentially atomic characteristic.