First-principles theoretical study on the electronic properties of theB32intermetallic compound LiAl

The electronic properties of the ordered LiAl crystal are studied within the self-consistent (non-muffin-tin) numerical-basis-set approach to the local-density formalism. The material appears to be electronically a semimetal with an electron pocket near $X$ (along $\Delta$) and a hole pocket at $\Gamma$. The band structure and density of states have characteristics similar to that of the tetrahedrally bonded IV-IV semiconductors (LiAl has a $T_d$ site symmetry); however, the indirect ${\Gamma }_{{25}^{\prime }}-X_1$ band gap (which decreases progressively as one goes along the diamond, Si, Ge, and $\alpha -\mathrm{Sn}$ series) becomes negative in LiAl. A study of charge redistribution effects indicates that while the Li-Al bond is an ionically polarized covalent bond, the Al-Al bonds are metalliclike and the Li-Li bonds are essentially nonbonding. Wave-function population analysis indicates that the bottom of the occupied valence band is of predominantly $\mathrm{Li} 2s$ character (hybridized with $\mathrm{Al} 3s$), while at higher energies the $\mathrm{Li} 2s$ character is reduced in favor of the Li and $\mathrm{Al} p$ character, which are dominant around the Fermi energy. The main intrasite-charge-redistribution effects involve pronounced $\mathrm{Li} 2s$ to $\mathrm{Li} 2p$ promotion (with a smaller $s-p$ promotion on the Al site) while the intersite (ionic) redistribution effects are found to be small. The observed trends in the measured Knight shifts (relative to the pure constituent metals) as well as the small paramagnetism and its dependence on the Li concentration are discussed in terms of these bonding effects. The abrupt changes in the differential electrical resistivity at ∼ 100°K is tentatively assigned to a structural instability induced by electron-hole interaction effects.