MODELING OF HALF-HEUSLER CRYSTALS WITH THE CHALCOPYRITE STRUCTURE: Li2MgZnX2 (X = N, P, As, Sb)

A model of Li2MgZnX2 half-Heusler compounds with the chalcopyrite structure is considered. The electronic structure is studied from first principles, showing that Li2MgZnX2 are direct-gap crystals, except for pseudo-direct-gap Li2MgZnP2, with a band gap of 2.7 eV, 2.2 eV, 3.3 eV, and 2.5 eV for X = N, P, As, and Sb, respectively. The band structure and chemical bonding in the model crystals are found to be similar to those in LiMgX and LiZnX half-Heusler crystals. Total electron density and deformation electron density distributions are obtained. It is found that Mg-X and Zn-X ionic-covalent bonds are stronger than Li-X ionic bonds in Li2MgZnX2 crystals, which allows Li atoms to move in the space between MgX4 and ZnX4 cation tetrahedra.