Subtle energies in density functional theory: Correlation and molecular dissociation

Abstract

AbstractIn nonrelativistic theory, heavy atoms with atomic number Z have binding energies that can be analyzed into a sum of decreasing terms: (i) the Hartree energy αZ7/3, (ii) a “boundary correction” αZ2 due to Scott, and (iii) exchange energy in the Dirac‐Slater approximation αZ5/3. Correlation varies grossly linearly with Z and a density functional interpretation is proposed. Generalization to diatomic molecules is then considered, the total overlap population being now an important ingredient. Both heteronuclear and homonuclear molecules 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 March, in light molecules with N electrons, D/N2 is connected with the von Weizsäcker inhomogeneity kinetic energy Tw; 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 relating D/N2 with Tar is obtained. Finally, for the valence electrons only in alkali metal clusters, D/N is related to Tw using pseudopotential calculations. © 1995 John Wiley & Sons, Inc.