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Based on our structural model and a tight-binding Hamiltonian the electronic structure of the superconductor YBa{sub 2}Cu{sub 3}O{sub 7} has been calculated by the use of a recursion method. Compared with the single crystal, we mainly analyzed the feature of the electronic structure showing the twin boundary and evaluated the probability of various configurations of Cu and O ions, the type of the hybridization bonds, and various (Cu-O){sup +} complexes in superconducting ceramics. Meanwhile, we indicate that the twin boundary may be closely related to an electron deficiency.

The electronic structure of γ′ phase in nickel-base superalloy containing impurity Zr is studied in the paper. Based on the model presented, we calculated the energy levels, the density of states, the partial-wave local density of states and the charge transfer of the system by use of the SCF-Xα-SW method. We compared the properties of Ni6AlZr with those of Ni6Al2. The result shows that the nonbonding peaks decrease evidently, some new stable bonding orbitals appear in the lower energy region, the unoccupied orbitals move towards high energy region and the energy gap increases, which all indicate that the γ′ phase is intensified and is more stable after Zr instead of Al in the system. The result of charge transfer shows that the Zr atom loses outer electrons, which is of benefit for the Zr atom to dissolve in the γ′ phase.

Based on related experiments, in this paper a model is presented to study the electronic structure of an impurity--stacking-fault complex. Using the tight-binding Hamiltonian and recursion method, we have calculated the electronic structure of systems containing an impurity--stacking-fault complex. Based on the calculation of the structural energy, the relation between impurity and stacking-fault energy was given. It found that impurity oxygen increased the stacking-fault energy of the Ni system, whereas impurity Fe decreased it markedly, which has been proved by our electron-microscope experiments. Calculations of the partial-wave integral local density of states for atoms give information on the local charge transfer and hybridized orbital.

The electronic structure of a boron-iron alloy was investigated theoretically by the self-consistent-field X\ensuremath{\alpha} scattered-wave method. A model cluster containing the light-impurity\char21{}vacancy complex B-V-B was presented for consideration of the effect of size, the character of the chemical bond, and other related experimental facts. Energy levels, density of states, partial-wave local density of states, transition states, and one-electron properties such as charge distribution and the Hellmann-Feynman force have been obtained. Based on the calculation, the concept of the ``efficient neighbor'' as a result of local structure was introduced. The calculation shows that the B-V-B model reflects the effect of the light impurity boron in the B-Fe alloy system, explains the mechanism of the B-V-B complex in the host, and indicates that the effect of the B-V-B complex is very localized.