Atomic transferability within the exchange-correlation density

Starting from either the exchange or the exchange-correlation density toget her with Bader's definition of an atom in a molecule, an atomic hole densit y function can be defined. Contour maps of atomic hole density functions ar e able to show how the electron density of each atom in a molecule is parti ally delocalized into the rest of atoms in the molecule. The degree of delo calization of the atomic density ultimately depends on the nature of the at om 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 e nvironments. In this article, contour maps for the N atom in the (N-2, CN-, NO+) series and the O atom in the (CO, H2CO, and HCOOH) series are present ed at the Hartree-Fock and CISD levels of theory. Moreover, the transferabi lity of N and O within the two series is studied by means of atomic similar ity measures. O 2000 John Wiley & Sons, Inc.