Theoretical site- and symmetry-resolved density of states and experimentalEELS near-edge spectra of AlB2 and TiB2

We report the orientation dependent B K-edge electron-loss near-edge spectr oscopy spectra of the isoscructural compounds AlB2 and TiB2. The observed d ifferences between the experimental spectra of the borides are discussed in terms of the variation in bonding between the two materials. The orientati on dependence is rationalized in terms of the anisotropic nature of the com mon crystal structure. For a detailed comparison with experiment, we have e mployed a first-principles method for the calculation of the partial densit y of states. This method is based on band calculations using the full-poten tial linearized augmented plane-wave method within density-functional theor y. We ascribe the origin of the discrepancies between the broadened ground- state density of states and experiment to the presence of a core hole in th e final state. The core-hole effect is self-consistently accounted for via the use of ab initio supercell calculations, lending to improved agreement with experiment particular in certain crystallographic directions, where sc reening of the core hole is expected to be much reduced. Additionally a det ailed analysis of the valence-band structure, charge-transfer effects, and covalency in the diborides has been undertaken.