First-Principles Study of Electronic and Vibrational Properties of BaHfN
arXiv:1007.4574 · doi:10.1103/PhysRevB.82.155125
Abstract
The transition metal nitride BaHfN, which consists of weakly bonded neutral slabs of closed shell ions, has structural and chemical similarities to other layered nitrides which have impressive superconducting T when electron doped: AHfNCl, AZrNCl, ATiNCl, with , and K, respectively for appropriate donor (A) concentrations . These similarities suggest the possibility of BaHfN being another relatively high T nitride upon doping, with effects of structure and the role of specific transition metal ions yet to be understood. We report first-principles electronic structure calculations for stoichiometric BaHfN using density functional theory with plane-wave basis sets and separable dual-space Gaussian pseudopotentials. An indirect band gap of 0.8 eV was obtained and the lowest conduction band is primarily of Hf 5 character, similar to -ZrNCl and -TiNCl. The two N sites, one in the Hf layer and another one in the Ba layer, were found to have very anisotropic Born effective charges (BEC):deviations from the formal charge (-3) are opposite for the two sites, and opposite for the two orientations (in-plane, out of plane). LO-TO splittings and comparison of BECs and dielectric constant tensors to those of related compounds are discussed, and the effect of electron doping on the zone-center phonons is reported.
11 pages, 5 figures