New insight into the intrinsic instability of fcc ZrH sub(2) by energy-resolved local bonding analysis

The electronic-driven instability of fcc ZrH sub(2) due to the reduction of density of states (DOS) at E sub(F) under the tetragonal distortion were used to be explained by Jahn-Teller effect or the shift of von Hove singularity. Here we explain this intrinsic instability with energy-resolved local bonding analysis by means of first-principles calculations. Our local bonding analysis reveals that this intrinsic instability stems from the peak of T sub(2g) and E sub(g) orbitals at E sub(F) with the former contributing much more. Tetragonal distortion lifts the T sub(2g) and E sub(g) degenerate orbitals, causing the change to local Zr-H and Zr-Zr bonding. These two fct structures share similar Zr-H bonding but different Zr-Zr bonding due to the different Zr-Zr distances. For all these three structures, Zr-4s and 4p electrons do not contribute to any bonding but partially Zr-5s electrons participate in the Zr-H bonding. We discuss the hybridization of Zr and H orbitals for these three ZrH sub(2) structures. Presented calculations support the Jahn-Teller type effect and provide a comprehensive understanding of the intrinsic instability of Zr dihydrides.