Electronic structure and positron annihilation inLaB6andCeB6

The energy-band structures for ${\mathrm{LaB}}_6$ and ${\mathrm{CeB}}_6$ are calculated by the full-potential linearized augmented-plane-wave (FLAPW) method on the basis of the local-density approximation. The results of the FLAPW band calculations are applied for the calculations of the three-dimensional Lock-Crisp-West (LCW) folded momentum densities (3D LCW FMD’s) of positron annihilation in ${\mathrm{LaB}}_6$ and ${\mathrm{CeB}}_6$ within an independent-particle model (IPM). The results are compared with the experimental ones reconstructed from two-dimensional angular correlation of positron-annihilation-radiation data by Tanigawa et al. Good agreement is observed in the general structures shown by the experimental and the theoretical 3D LCW FMD’s. It is indicated that the basic structures of the 3D LCW FMD in ${\mathrm{LaB}}_6$ are mainly determined by the Fermi-surface topology, and those in ${\mathrm{CeB}}_6$ are due not only to the Fermi-surface topology but also the characters of the electron states near the Fermi energy. The detailed comparison of the experimental results with the IPM ones by the FLAPW method leads to qualitative discussions over the IPM framework in the systems of ${\mathrm{LaB}}_6$ and ${\mathrm{CeB}}_6$.