Electronic, vibrational, superconducting and thermodynamic properties of cubic antiperovskite ZnNNi3

Abstract

We present results of ab initio theoretical investigations of the structural and electronic properties of the cubic superconductor ZnNNi3 by employing the plane wave pseudopotential method within the generalized gradient approximation. The density of states at the Fermi level is found to be governed by the Ni 3d electrons. A linear-response approach to the density functional theory is used to derive the phonon dispersion curves, vibrational density of states and the electron-phonon coupling parameter. The calculated electron-phonon coupling constant. and the lambda logarithmically averaged phonon frequency are calculated to be 0.654 and 169.89 K, respectively, giving the superconducting transition temperature T-C=2.925 K according to the Allen-Dynes formula. Our calculated value of T-C is in excellent accord with the corresponding experimental value of 3 K. Using the phonon dispersion results, we further present an assessment of important thermodynamical properties such as internal energy (E), Helmholtz free energy (F), constant-volume specific heat (C-V), entropy (S) and Debye temperature (Theta) in the framework of quasi harmonic approximation theory.