A MOMENTUM DISTRIBUTION FUNCTIONAL-APPROACH TO THE HUBBARD-MODEL AT HALF-FILLING

We investigate the half-filled Hubbard model in one and two dimensions using approximations to the energy expressed as functionals of the momentum distribution. The functionals are calculated using the Hartree-Fock approximation and density functional theory in the local-spin-density and self-interaction-corrected (sic) local-spin-density approximations (LSDA) by expressing the ground-state spin densities as a variational ansatz in which the momentum distribution enters as a variational quantity. We calculate the momentum distribution, energy and local moment, as well as our ansatz orbitals, in all three approximations and find that the SIC always improves upon the LSDA.