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Local density functional is investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method for ScN in the hexagonal structure and the rocksalt structure and for hexagonal structures linking a layered hexagonal phase with wurtzite structure along a homogeneous strain transition path. It is found that the wurtzite ScN is unstable and the layered hexagonal phase, labelled as ho, in which atoms are approximately fivefold coordinated, is metastable, and the rocksalt ScN is stable. The electronic structure, the physical properties of the intermediate structures and the energy band structure along the transition are presented. It is found that the band gaps change from 4.0 to 1.0 eV continuously when c/a value varies from 1.68 to 1.26. It is noticeable that the study of ScN provides an opportunity to apply this kind of material (in wurtzite[h]-derived phase).

The discrete variational method within the framework of density functional theory is used to study the effect of zirconium on the electronic structure of the grain boundary in . The results for the interatomic energies show that the strength of the grain boundary is increased by the substitution of Zr for Al. The calculation of the charge distribution indicates that the directionality of the bonds in the grain boundary region is weakened by the addition of Zr. These results show that the alloying effect of Zr introduced into can significantly improve the ductility of , while strengthening the grain boundary.

The electronic structure of and grain boundaries in containing B are investigated by the use of the discrete variational method. The effects of B on grain boundaries are discussed. The results show that B forms stronger bonding states with its neighbouring host atoms, and it can be expected that the cohesive strength of the grain boundaries will be increased.

Based on our structural model and a tight-binding Hamiltonian the electronic structure has been calculated by use of a recursion method (RM) for two models of the tetragonal DO 22 and the cubic Ll 2 crystal structure in Al 3 Ti + X ( X = Mn , Fe or Cu ) for contrast. The results show that the binary Al 3 Ti is stabilized in the DO 22 structure, and the alloying element (AE) X is found to strongly favor Al site and to promote the stability of the Ll 2 structure, in agreement with the experiment. The transform of the crystal structure from the DO 22 to the Ll 2 may be induced by the constriction of the lattice constant c and the elongation of the lattice constant a after the AE X replaces Al for the DO 22 . The result also shows that the Ll 2 structure in the Al 3 Ti + X alloys has the strong directional bonds which may cause the material to be brittle.

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 the tight-binding bond recursion method, the energetics parameters of ∑3[111] grain boundary in nickel are investigated. The theoretical results indicate that the boron enhances interatomic energy between the host atoms, and between impurity and nickel atoms. Calculations of the energy of the grain boundary segregation show that boron, nitrogen, and phosphorus have the tendency to segregate onto the grain boundary and segregation property of boron is stronger than that of nitrogen and phosphorus.

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.