Atomic transferability within the exchange-correlation density

Starting from either the exchange or the exchange-correlation density together with Bader’s definition of an atom in a molecule, an atomic hole density function can be defined. Contour maps of atomic hole density functions are able to show how the electron density of each atom in a molecule is partially delocalized into the rest of atoms in the molecule. The degree of delocalization of the atomic density ultimately depends on the nature of the atom studied and its environment. Atomic hole density functions are also used to define an atomic similarity measure, which allows for the quantitative assessment of the degree of atomic transferability in different molecular environments. In this article, contour maps for the N atom in the (N2, CN−, NO+) series and the O atom in the (CO, H2CO, and HCOOH) series are presented at the Hartree–Fock and CISD levels of theory. Moreover, the transferability of N and O within the two series is studied by means of atomic similarity measures. c © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1361–1374, 2000