SUBTLE ENERGIES IN DENSITY-FUNCTIONAL THEORY - CORRELATION AND MOLECULAR DISSOCIATION

In nonrelativistic theory, heavy atoms with atomic number Z have bindi ng energies that can be analyzed into a sum of decreasing terms: (i) t he Hartree energy alpha Z(7/3), (ii) a ''boundary correction'' alpha Z (2) due to Scott, and (iii) exchange energy in the Dirac-Slater approx imation alpha(S/3). Correlation varies grossly linearly with Z and a d ensity functional interpretation is proposed. Generalization to diatom ic molecules is then considered, the total overlap population being no w an important ingredient. Both heteronuclear and homonuclear molecule s are treated. Attention is then focused on the molecular dissociation energy D: a further ''subtle'' quantity for density functional theory because of Teller's theorem. Following the proposal of Mucci and Marc h, in light molecules with N electrons, D/N-2 is connected with the vo n Weizsacker inhomogeneity kinetic energy T-w; this motivates a brief discussion of scaling properties of this latter quantity. Generalizing the treatment of atomic energies outlined above, the 1/6 power law re lating D/N-2 with T-w is obtained. Finally, for the valence electrons only in alkali metal clusters, D/N is related to T-w using pseudopoten tial calculations. (C) 1995 John Wiley & Sons, Inc.