We have performed accurate ab initio total energy calculations using the fullpotential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential to systematically investigate elastic properties of 18 stable, meta-stable and hypothetical hexagonal (AlB 2 -like) metal diborides MB 2 , where M = Na, Be, Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ag and Au. For monocrystalline MB 2 the optimized lattice parameters, independent elastic constants (C ij ), bulk modules (B), shear modules (G) are obtained and analyzed in comparison with the available theoretical and experimental data. For the first time numerical estimates of a set of elastic parameters of the polycrystalline MB 2 ceramics (in the framework of the Voigt-Reuss-Hill approximation), namely bulk and shear modules, compressibility (β), Young's modules (Y), Poisson's ratio (ν), Lamé's coefficients (μ, λ), are performed.

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The full‐potential linearized augmented plane wave method with the generalized gradient approximation for the exchange and correlation potential (LAPW‐GGA) is used to understand the electronic and elastic properties of the first thorium‐containing nitride perovskite TaThN3. Total and partial density of states, charge distributions as well as the elastic constants, bulk modulus, compressibility, shear modulus, Young modulus and Poisson ratio are obtained for the first time and analyzed in comparison with cubic ThN. The chemical bonding in TaThN3 is a combination of ionic Th–N and of mixed covalent–ionic Ta–N bonds. The cubic TaThN3 is semiconducting with the direct gap at about 0.65 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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