The Structure and Elastic and Thermodynamic Properties of Cubic-NbH2 under High Pressures from First-Principles Calculations

NbH2 hydride is an important material in hydrogen storage materials. However, until now there have been no experimental and theoretical data on the elastic and thermodynamic properties. The structure and thermodynamic properties of cubic-NbH2 under high temperatures and pressure are investigated by first-principles study based on the pseudo-potential plane-wave density functional theory method using the generalized gradient approximation and quasi-harmonic Debye model. The results show that the calculated structural parameters of NbH2 are in good agreement with the available experimental results and other theoretical data. The obtained elastic constants satisfy the requirement for mechanical stability, indicating that the NbH2 crystal is stable in the investigated pressure and temperature ranges. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the thermodynamic properties of NbH2, such as the thermal expansion coefficient and the heat capacity dependence of temperature and pressure in the ranges 0-1100K and 0-70GPa, are also obtained, respectively.