Local-density-functional calculations have been performed to study the electronic structure and magnetism of 3d transition-metal ions (Cr, Mn, Fe, Co, and Ni) substituting for the Cu ion in La2 Sr Cu04. These systems are simulated by small clusters which are surrounded by over 5000 point charges. It is found that all the substituting ions possess local magnetic moments. Through a systematic comparison we find that the Cu-0 system has the smallest p-d separation and the largest p-d hybridization. The Cu-0 system has the smallest local magnetic moment, which can be reduced to zero by hole doping. We also find that removing an electron from these systems further increases the p-d hybridization. The crystal-field splittings of these transition-metal oxide systems are found to remain nearly constant at about 0.1 Ry, while the Jahn-Teller splittings vary considerably, depending on the manner in which single-particle levels are filled. Hyperfine fields have been calculated for the Fe ion at both trivalent and divalent states. These calculations are compared with available experimental measurements.
We report a density-functional study of two copper-oxygen clusters (Cu06 ' and Cu30, 6 ) that are present in La2 Sr"Cu04. All-electron, self-consistent, spin-polarized calculations are performed by using the linear combination of Gaussian orbitals method. Several charge states of these clusters are considered in order to study the effects of doping. Results are presented for the charge and spin densities and total and partial density of states. These clusters have local moments on the Cu atoms. Our results indicate strongly covalent bonding between copper and oxygen. Transitionstate calculations are made to study the electron-electron correlations and charge-transfer transitions. The parameters of a model Hamiltonian are determined. We have performed some nonlocal spin-density-functional calculations for the Cu06 cluster to study the efFects of self-interaction corrections. Both the size of the local moment and the exchange splitting are increased by the use of the nonlocal corrections.
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