We introduce in this work a new approach to the identification of localized electronic groups in atomic and molecular systems. Our approach is based on local behavior of the Hartree–Fock parallel-spin pair probability and is completely independent of unitary orbital transformations. We derive a simple ‘‘electron localization function’’ (ELF) which easily reveals atomic shell structure and core, binding, and lone electron pairs in simple molecular systems as well.

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Studies of electronic structure of solids have concentrated mainly on Hilbert space properties such as energy-band structures and density of states, as well as some properties that can be reduced from them. Here, we report application of the topological charge density analysis to crystals. It is found that the pseudoatoms (or nonnuclear attractors, which are charge accumulations in nonnuclear regions), first found in Liz, exist in solid lithium and sodium as well. In the former, the pseudoatoms form a connected network; in the latter, they are separated from one another. Although such networks obey the space group symmetry of the corresponding crystal, their existence is an intrinsic property of a specific crystal. 0 1993 John Wiley

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 Li 2 , Na2' Na4, and Nas. The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of -V 2 p(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 molt~cule to remove an essentially atomic characteristic.