Strong correlation effect on the thermodynamic and mechanical properties of ytterbium dihydride

The strong correlation effect of the thermodynamic and mechanical properties of the Pnma and Fm-3m phases of ytterbium dihydride (YbH2) has been investigated using density functional theory plus Hubbard U method. The equilibrium geometries, elastic constants, various moduli, Poisson's ratio, and elastic wave velocities of the two phases of YbH2 are systematically studied. The Pnma and Fm-3m phases of YbH2 exhibit brittle characteristics. Phonon calculations verify that the two phases are thermodynamically stable. The low-frequency region of the two phases share similar features, whereas the high-frequency region shows a remarkable difference between the two phases. Given the phonon contribution to the Helmholtz free energy, the temperature dependences of equilibrium volume, bulk modulus, entropy, and heat capacity at constant pressure are obtained using quasiharmonic approximation. The calculated trends of equilibrium volume and head capacity at constant pressure are consistent with experimental data.