Structural, electronic, elastic properties and chemical bonding in LaNi2P2 and LaNi2Ge2 from first principles

By means of first-principles calculations, we have systematically studied the structural, elastic, electronic, and thermodynamic properties of two related layered 122-type intermetallics: tetragonal LaNi2P2 and LaNi2Ge2. The optimized lattice constants, cell volumes, electronic bands, Fermi surface topology, and densities of states were obtained and analyzed. We found that the bonding picture in the examined phases is of a complex anisotropic character and can be described as a mixture of metallic, ionic, and covalent contributions. We predicted that LaNi2P2, and LaNi2Ge2 are mechanically stable and relatively soft materials with high compressibility and rather small hardness. Both phases will exhibit comparable elastic anisotropy and behave in a brittle manner. Sound velocities, Debye temperatures, and heat capacity Cp(T) were evaluated for LaNi2P2 and LaNi2Ge2 in the low-temperature limit, and are in reasonable agreement with available experiments.