Can an independent-electron model be exact for an N-electron system?

Abstract

Density functional theory (DFT) is commonly understood to provide an exact independent-electron model of N-electron ground states, using only local potential functions. It has recently been shown that restriction to local potentials leads to inconsistencies in the Thomas-Fermi theory, in the Hartree-Fock model of DFT (local exchange potential), and in linear response theory (the exchange response kernel differs from the exact linear exchange operator derived in 1930 by Dirac). It is shown here that by extending the theory to a more general orbital functional theory (OFT) these inconsistencies or paradoxes can be resolved. An orbital-functional representation of correlation energy leads to a formally exact theory of stationary states and of linear response. The theory is free of self-interaction and implies physically meaningful one-electron energies, consistent with Landau quasiparticles in many-body theory.