Relationships between bond dissociation energies, electron density minima and electrostatic potential minima

The experimental dissociation energies of a group of homonuclear diatomic molecules are found to correlate with computed electron densities ρ(r) and electrostatic potentials V(r) at the bond midpoints, supporting an earlier prediction based on density functional arguments (N. H. March, P. M. Kozlowski and F. Perrot 1990, J. molec. Struct. Theochem, 209, 433). The relationships are generalized to 45 molecules of various types, focusing upon the minima of ρ(r) and V(r) along internuclear axes. Dissociation energies are shown to be related distinctly more closely to the minimum values of V(r) than to those of ρ(r). This complements previous findings for negative monatomic ions as well as the recent observation that the V(r) minima provide the more realistic boundary points between bonded atoms (relative to literature values of covalent radii), and thus further establishes the significance of electrostatic potential axial minima with respect to covalent bonding. In the present work, all calculations were carried out by a density functional procedure (Becke exchange, Lee, Yang and Parr correlation, 6-31G** basis sets).