First-principles study of elastic, electronic, and optical properties of α-TeO2 under pressure

Crystalline α-TeO₂ was investigated at ambient pressure using ab initio calculations. The effect of pressure on α-TeO₂ was studied from 0 to 10 GPa. The lattice parameters and elastic constants calculated by LDA and GGA method at 0 GPa both agree with the available theoretical and experiment results. The elastic constants C_ij, the bulk modulus B, the shear modulus G, Young's modulus E, and the ductile and brittle character (B/G) were calculated and examined in detail. It was found that the calculated universal anisotropy index indicated that α-TeO₂ has anisotropy under 0 GPa, and with the pressure increases, its elastic anisotropy increases. Furthermore, from the mechanical stability criteria, it is show that the structure of tetragonal α-TeO₂ is not stable above 5.1 GPa. Finally, the electronic and optical properties were also investigated, and the results show that, on increasing the external pressure, the energy bandgap increases, with the optical spectrum exhibiting anisotropy in the x and z directions and a small blue shift under pressure.