Abstract: | The correlation energy functional Ec of the Hartree-Fock density is investigated. It was previously established that Ec produces the exact ground-state energy when added to the Hartree-Fock energy. Except when certain degeneracies occur, it is here shown that Ec is bounded from below when the coordinates of the Hartree-Fock density are scaled uniformly by λ, as λ → ∞. Consequently, approximations to Ec should display this bounded property, which is a second-order perturbation energy. It is also shown that a corresponding result applies to that correlation energy functional, Ëc, which is to be added to a completed exact exchange-only (in the OPM sense) density functional calculation. Scaling requirements are presented for each order in the perturbation expansion for Ëc. For instance, the second-order term is dimensionless. © 1997 John Wiley & Sons, Inc. |