First-principles study of ground state properties of ZrH2

Structural, mechanical, electronic, and thermodynamic properties of fluorite and tetragonal phases of ZrH2 are systematically studied by employing the density functional theory within generalized gradient approximation. The existence of the bistable structure for ZrH2 is mainly due to the tetragonal distortions. And our calculated lattice constants for the stable face-centered tetragonal (fct) phase with c/a = 0.885 are consistent well with experiments. Through calculating elastic constants, the mechanically unstable characters of face-centered cubic (fcc) phase and fct structure with c/a = 1.111 are predicted. As for fct0.885 structure, our calculated elastic constants explicitly indicate that it is mechanically stable. Elastic moduli, Poisson’s ratio, and Debye temperature are derived from elastic constants. After analyzing total and partial densities of states and valence electron charge distribution, we conclude that the Zr–H bonds in ZrH2 exhibit weak covalent feature. But the ionic property is evident with about 1.5 electrons transferring from each Zr atom to H. Phonon spectrum results indicate that fct0.885 structure is dynamically stable, while the fcc and fct1.111 structures are unstable in accord with the mechanical stability analysis.

► Mechanical properties of ZrH2 are systematically predicted. ► The main distinction of covalent and ionic chemical bonding nature is determined. ► Dynamical stability of phases of ZrH2 are analyzed by the phonon spectrum.