G. Esirgen et Ne. Bickers, FLUCTUATION-EXCHANGE THEORY FOR GENERAL LATTICE HAMILTONIANS, Physical review. B, Condensed matter, 55(4), 1997, pp. 2122-2143
The fluctuation-exchange or FLEX, approximation for interacting electr
ons is derived for lattice Hamiltonians with general instantaneous one
- and two-body terms. The use of a two-body basis set indexed by relat
ive separation, rather than relative momentum, is emphasized. The fluc
tuation-exchange approximation for the three-orbital CuO2 model with o
n-site and near-neighbor Coulomb interactions is solved for one-partic
le properties. Unit-cell densities corresponding to both ''hole doping
'' and ''electron doping'' are studied. The model is found to be far f
rom a charge-density instability for all reasonable parameter values.
The only nearly unstable particle-hole channel for unit-cell densities
close to unity has Q similar to(pi,pi) and S=1 (antiferromagnetic). T
he Fermi surface of the interacting system is computed, and the Luttin
ger theorem verified numerically in its most general context. Orbital-
projected occupancy factors and spectral densities an examined.