First-principles study of structural and electronic properties of multiferroic oxide Mn₃TeO₆ under high pressure

Mn₃TeO₆ (MTO) has been experimentally found to adopt a P2₁/n structure under high pressure, which exhibits a significantly smaller band gap compared to the atmospheric $R\overline{3}$ phase. In this study, we systematically investigate the magnetism, structural phase transition, and electronic properties of MTO under high pressure through first-principles calculations. Both $R\overline{3}$ and P2₁/n phases of MTO are antiferromagnetic at zero temperature. The $R\overline{3}$ phase transforms to the P2₁/n phase at 7.58 GPa, accompanied by a considerable volume collapse of about 6.47%. Employing the accurate method that combines DFT+U and GW, the calculated band gap of $R\overline{3}$ phase at zero pressure is very close to the experimental values, while that of the P2₁/n phase is significantly overestimated. The main reason for this difference is that the experimental study incorrectly used the Kubelka–Munk plot for the indirect band gap to obtain the band gap of the P2₁/n phase instead of the Kubelka–Munk plot for the direct band gap. Furthermore, our study reveals that the transition from the $R\overline{3}$ phase to the P2₁/n phase is accompanied by a slight reduction in the band gap.