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We describe a method for calculating, within density functional theory, theelectronic structure associated with typical defects which substitute for Cu inthe CuO2 planes of high-Tc superconducting materials. The focus is primarily onBi2Sr2CaCu2O8, the material on which most STM measurements of impurityresonances in the superconducting state have been performed. The magnitudes ofthe effective potentials found for Zn, Ni and vacancies on the in-plane Cusites in this host material are remarkably consistent with phenomenologicalfits of potential scattering models to STM resonance energies. The effectivepotential ranges are quite short, of order 1 A with weak long range tails, incontrast to some current models of extended potentials which attempt to fit STMdata. For the case of Zn and Cu vacancies, the effective potentials arestrongly repulsive, and states on the impurity site near the Fermi level aresimply removed. The local density of states (LDOS) just above the impurity isnevertheless found to be a maximum in the case of Zn and a local minimum incase of the vacancy, in agreement with experiment. The Zn and Cu vacancypatterns are explained as due to the long-range tails of the effective impuritypotential at the sample surface. The case of Ni is richer due to the Ni atom'sstrong hybridization with states near the Fermi level; in particular, the shortrange part of the potential is attractive, and the LDOS is found to varyrapidly with distance from the surface and from the impurity site. We proposethat the current controversy surrounding the observed STM patterns can beresolved by properly accounting for the effective impurity potentials andwave-functions near the cuprate surface. Other aspects of the impurity statesfor all three species are discussed.Comment: 37 pp. pdf including figures, submitted to Phys. Rev.

Ab initiocalculation of impurity effects in copper oxide materials