FLUCTUATION EXCHANGE ANALYSIS OF SUPERCONDUCTIVITY IN THE STANDARD 3-BAND CUO2 MODEL

The fluctuation exchange, or FLEX, approximation for interacting elect rons is applied to study instabilities in the standard three-band mode l for CuO2 layers in the high-temperature superconductors. Both intrao rbital and near-neighbor Coulomb interactions are retained. The fillin g dependence of the d(x2-y2) transition temperature is studied in both the ''hole-doped'' and ''electron-doped'' regimes using parameters de rived from constrained-occupancy density-functional theory for La2CuO4 . The agreement with experiment on the overdoped hole side of the phas e diagram is remarkably good, i.e., transitions emerge in the 40 K ran ge with no free parameters. In addition the importance of the ''orbita l antiferromagnetic,'' or flux phase, charge density channel is emphas ized for an understanding of the underdoped regime.