Elasticity, ideal tensile strength and lattice dynamics of LuH2 dihydride from first-principles investigations

Abstract

The structure, elasticity, tensile strength, phonon and thermodynamic properties of LuH2 with CaF2 structure have been investigated by using first-principles approach. The calculated lattice parameters and the single-crystal elastic constants of LuH2 agree well with experimental data and other theoretical results in the literature. The polycrystalline moduli of LuH2 involving volume elastic modulus, Young's modulus, and shear modulus, the brittle/ductile properties, Poisson's ratio, Debye temperature, sound velocities and hardness have been predicted. Also, the elastic anisotropy has been evaluated. The tensile strength along [100] crystallographic direction has been obtained using first principles total energy method. In addition, the phonon dispersion curves and the corresponding phonon density of states of LuH2 have been determined by virtue of a linear-response approach to density functional perturbation theory (DFPT) along with the small displacement method successfully, and the Infrared-active modes and the Raman-active modes at the Brillouin zone center have been analyzed according to the group theory. Finally, the lattice entropy and the lattice constant volume specific heat up to 1500 K have also been estimated based on quasi-harmonic approximation (QHA).