Total-energy calculations for intermetallic compounds with a first-principles linear combination of atomic orbitals method

For the compounds LiMg and LiAl the difference in the total energy in the B2 (CsCl) and B32 (NaTl) crystal structures has been calculated with use of a first-principles linear-combination-of-atomic-orbitals method. The calculations have been performed as a function of volume---this allows determination of the volume and the heat of formation for each of the compounds. At zero pressure the correct stable structure and a reasonable value for the heat of formation is found for each of the compounds. The bonding characteristics are studied by analyzing the electron-density distributions and the difference electron densities. For LiMg (B2) the bonding is found to be predominantly metallic, while for LiAl (B32) the formation of an Al---Al ``bond charge'' points to an at least partially covalent character of the chemical bond.