TOPOLOGY OF ELECTRON-ELECTRON INTERACTIONS IN ATOMS AND MOLECULES .1.THE HARTREE-FOCK APPROXIMATION

Topologies of the electron intracule and extracule densities, I(R) and E(R), are analyzed. These topologies are found to be inherently more complex than those of the one-electron density. The main topological f eatures of I(R) and E(R) are already present in the densities calculat ed within the Hartree-Fock (HF) approximation. Results of test calcula tions on several planar systems show that the positions and properties of attractors in I(R) and E(R) are predicted with a surprising fideli ty by a naive independent-atom model, making it possible to index dist inct types of electron pairs present in atoms and molecules. In genera l, each pair of atoms in a given molecule has the potential of produci ng a pair of attractors in I(R). At the HF level of theory, all the at oms collectively furnish a single attractor in I(R) at R=0, but this t opological pattern is bound to change upon the inclusion of electron c orrelation. The attractors in E(R) stem from both individual atoms and atomic pairs. In addition, attractors that are not associated with ei ther of these entities are observed. The plethora of attractors presen t in I(R) and E(R) give rise to complicated patterns of other critical points. Unusual. topological features, such as attractors linked by m ultiple interaction lines and bifurcations at bond points, are also en countered. (C) 1996 American Institute of Physics.