Electron localization on dislocations in metals: Real-space first-principles calculations

The electronic structure of different types of dislocations in B2 intermetallic NiA1 and bcc transition metals was investigated using the first-principles real space tight-binding linear-muffin-tin-orbital recursion method. An unusual localization of electronic states inside the valence band is observed in the cores of 〈100〉(010) and 〈100〉(011) edge dislocations but not in 〈111〉(011) edge dislocations. The nature of these localized electronic states and mechanisms for their appearance are analyzed. We show that conditions of electron localization are (i) a decrease of the number of nearest neighbors ("broken bonds") around the central atom of the dislocation core, (ii) a specific local symmetry of the atomic arrangement in the region of the dislocation core, and (iii) the contribution of d states to the formation of these interatomic bonds. We illustrate our conclusions by demonstrating that electron localization also occurs in 〈100〉(010) edge dislocations in bcc metals W, Fe, and Ni. In contrast to semiconductors, the electron localization in metals takes place on bonding orbitals, and will therefore have a significant impact on dislocation energetics and chemical bonding. We suggest that localized electronic states can give a significant contribution to impurity-dislocation interactions in NiA1 and other B2 intermetallics such as CoTi, CoHf, and CoZr.