Abstract
To study the high pressure behavior of metal tetrahydrides, here, we apply the first-principles method to study the influence of pressure on the structural stability, mechanical, electronic and optical properties of two TMH4 (TM = Ti and V) tetrahydrides. The calculated results show that although the formation enthalpy of two TMH4 increases with increasing pressure, two TMH4 tetrahydrides are thermodynamic stability under high pressure. In particular, the VH4 has better thermodynamic stability in comparison to TiH4 under pressure. Furthermore, the calculated elastic modulus of TMH4 increases with increasing pressure. The VH4 has strong deformation resistance and high elastic stiffness in comparison to TiH4 under pressure. Essentially, the structural stability and mechanical properties of TiH4 and VH4 are related to the formation of TM-H bond in TMH4. However, the pressure weakens the shear deformation resistance and elastic stiffness of TMH4 when the pressure is bigger than 70 GPa. In addition, two TMH4 tetrahydrides show electronic properties. In particular, the pressure enhances the electronic interaction of TiH4 and VH4 near the Fermi level, which is beneficial to store a mass of hydrogen. Finally, it is found that the pressure induces the main peak of TMH4 to occur migration from low energy region to the high energy region.
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