The scalar relativistic contributions to bond or atomization energies of homo- or hetero-polar s-p-bonded atoms, Δ~(rel)E(bond), correlate well with the changes on bond formation of the electron density, integrated throughout the spatial K-shell region of the heavy nucleus, Δ~(bond)ρK_(-region), times Z~4, where Z is the nuclear charge. The "bond density changes" in the innermost atomic core regions, however, have no direct simple relationship to the electron density reorganizations in the outer atomic valence shell regions, which determine the nonrelativistic main contribution to the bond energy, Δ~(nonrel)E(bond). Also, scalar relativistic bond energy changes and bond length changes, Δ~(rel)R_e, are not directly correlated. Namely, 250L(rel)E(bond) correlates with the difference Δ~(bond)ρK_(-region), whereas Δ~(rel)R_e correlates with the derivative (d_((ρK)_(region))/dR). Reducing the internuclear distance from the separated to the united atom limit through the equilibrium distance value, R_e, the density around the nucleus at first decreases in many cases, goes through a minimum, and finally increases again. Therefore (d_((ρK)_(-region))/dR) may be positive or negative at R_e.
展开▼
