Density functional (B3LYP/SDD/6-311＋＋G**) method with relativistic effective core potential (RECP) has been used to compute the microcosmic characters of YH₂, and to calculate energy E, thermodynamic functions of YH₂(D, T). Considering the characteristics of different motion types, the vibration energy and vibration entropies of the molecules were assumed to be the corresponding values of their solid states. ΔH^⊖, ΔS^⊖, ΔG^⊖ and hydrogen isotope equilibrium pressures of the hydrogenation reaction at different temperatures have been calculated based on this approximation. The enthalpy of formation of YH₂(s) at 298 K is 199.25 kJ•mol^－1 , Which is close to the experimental value 210.00 and 225.94 kJ•mol^－1. The results show that the present method is feasible to theoretical study on hydrogen storage materials.

Key words: YH₂, molecular structure, thermodynamic function