Electronic structure, phonons and electron-phonon interaction in MgXNi3 (X = B, C and N)

Abstract

Ab initio calculations have been performed to study the electronic structure, phonon dispersion relations, and the electron-phonon interaction for cubic superconductors MgXNi3 with X = B, C and N. The electronic calculations are based upon the application of a plane wave basis, ultrasoft pseudopotentials, and the local density approximation of the density functional scheme. The electronic structure results are used, within the implementation of a linear response technique, for calculations of phonon states. Our calculations predict anomalous dispersion of the transverse acoustic branch along [111] in MgCNi3, and of all the three acoustic branches in a larger region of the Brillouin zone for MgNNi3. An explanation for the differences in the phonon dispersion and electron-phonon coupling parameter between these three materials has been put forward.