Experimentally synthesized MoSi₂N₄ (Science 369 670 (2020)) is a piezoelectric semiconductor. Here, we systematically study the large biaxial (isotropic) strain effects (0.90–1.10) on electronic structures and transport coefficients of monolayer MoSi₂N₄ by density functional theory (DFT). With a/a ₀ from 0.90 to 1.10, the energy band gap firstly increases, and then decreases, which is due to transformation of conduction band minimum (CBM). Calculated results show that the MoSi₂N₄ monolayer is mechanically stable in the considered strain range. It is found that the spin-orbital coupling (SOC) effects on Seebeck coefficient depend on the strain. In unstrained MoSi₂N₄, the SOC has neglected influence on Seebeck coefficient. However, the SOC can produce important influence on Seebeck coefficient, when the strain is applied, for example, 0.96 strain. The compressive strain can change relative position and numbers of conduction band extrema (CBE), and then the strength of conduction bands convergence can be enhanced, to the benefit of n-type ZT _e. Only about 0.96 strain can effectively improve n-type ZT _e. Our works imply that strain can effectively tune the electronic structures and transport coefficients of monolayer MoSi₂N₄, and can motivate farther experimental exploration.

实验合成的 MoSi ₂ N ₄ ( Science 369 670 (2020)) 是一种压电半导体。在这里，我们通过密度泛函理论（DFT）系统地研究了大双轴（各向同性）应变效应（0.90-1.10）对单层MoSi ₂ N _{4的电子结构和输运系数的影响。}当a / a ₀从0.90 到1.10 时，能带隙先增大后减小，这是由于导带最小值（CBM）的变换。计算结果表明，MoSi ₂ N ₄单层在所考虑的应变范围内是机械稳定的。发现自旋轨道耦合（SOC）对塞贝克系数的影响取决于应变。在未应变的MoSi ₂ N ₄中，SOC忽略了对塞贝克系数的影响。然而，当施加应变时，SOC 会对塞贝克系数产生重要影响，例如 0.96 应变。压缩应变可以改变导带极值（CBE）的相对位置和数量，从而增强导带收敛的强度，有利于n型ZT _e。仅约0.96应变即可有效提高n型ZT _e. 我们的工作表明，应变可以有效地调整单层 MoSi ₂ N ₄的电子结构和传输系数，并可以激发进一步的实验探索。