Ab initiocalculations of the electronic structure and bonding characteristics ofLaB6

Abstract

Lanthanum hexaboride (${\mathrm{LaB}}_{6}$, NIST SRM--660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor $(f)$ and hence the diffracted intensities. The electronic structure and bonding properties of ${\mathrm{LaB}}_{6}$ have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas--van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the ${\mathrm{LaB}}_{6}$ compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the ${\mathrm{LaB}}_{6}$ system and partially explains its high efficiency as a thermionic emitter.