Structural, elastic and electronic properties of new antiperovskite-type superconductor ZnNNi3 from first-principles

A theoretical study of the structural, elastic and electronic properties of a new antiperovskite-type nitrogen-based superconductor ZnNyNi3, y = 1 012 +/- 0 208 has been performed on the stiochiometric compound, ZnNNi3, using the augmented plane waves plus local orbital (APW+lo) method within the framework of density functional theory This is compared with the isostructural non-superconducting ZnCNi3 The optimized structural parameters were determined using different exchange-correlation potentials. The calculated lattice constants are within the usual accuracy range of such calculations although the deviations of results obtained using the generalized gradient approximation proposed by Wu-Cohen(WC-GGA) are the least The independent elastic constants (C-11, C-12 and C-44) are evaluated and numerical estimates of elastic parameters of the polycrystalline compounds were obtained in the framework of the Voigt-Reuss-Hill approximations. These elastic parameters, some of which are found to be of comparable magnitude in both compounds, were used to examine their mechanical properties We found that the materials are brittle and with fairly high elastic anisotropy. The electronic band structures. total, site and orbital decomposed densities of states (DOS) were obtained and analysed. Our electronic structure results show that in ZnNNi3, states near the Fermi energy are dominated by Ni d and N p states This is also the case for ZnCNi3 The peak in the DOS due to Ni d(xz), d(yz) in ZnNNi3 is closest to the Fermi energy, and is about 0 21 eV away from the Fermi energy compared with an energy distance of 0.09 eV away of similar peak in ZnCNi3. resulting in decreased value of Fermi level density of states in ZnNNi3 We estimated the Debye temperature of both compounds from the calculated mean sound velocity Our results show that the stoichiometric ZnNNi3 and ZnCNi3 are very much alike in both structural and elastic properties but differ in electronic properties The agreement with available theoretical and experimental data is reasonable (C) 2010 Published by Elsevier B V.