Abstract The structure, elastic, electronic and optical properties of two-dimensional (2D) MI2 (M = Pb, Ge, Cd) under strain are systematically studied by the first-principles method. It is proved that the monolayer structure of 2D-MI2 is stable by phonon spectra. Moreover, the large ideal strain strength (40%), the large range of strain and the elastic constants of far smaller than other 2D materials indicate that the single-layer PbI2 and GeI2 possess excellent ductility and flexibility. By applying appropriate strain to the structure of 2D-MI2, the band gaps of single-layer MI2 can be effectively controlled (PbI2: 1.04 ∼ 3.03 eV, GeI2: 0.43 ∼ 2.99 eV and CdI2: 0.54 ∼ 3.36 eV). It is found that the wavelength range of light absorbed by these three metal iodides is 82–621 nm, so 2D-MI2 has great absorption intensity for ultraviolet light in a large wavelength range, and the strain of structure can effectively regulate the optical parameters.

中文翻译：

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应变作用下单层金属碘化物的结构、弹性和光学性质的第一性原理研究

摘要 采用第一性原理方法系统地研究了应变作用下二维(2D) MI2 (M = Pb, Ge, Cd)的结构、弹性、电子和光学性质。声子光谱证明2D-MI2的单层结构是稳定的。此外，大的理想应变强度（40%）、大的应变范围和远小于其他二维材料的弹性常数表明单层 PbI2 和 GeI2 具有优异的延展性和柔韧性。通过对 2D-MI2 结构施加适当的应变，可以有效控制单层 MI2 的带隙（PbI2：1.04 ∼ 3.03 eV，GeI2：0.43 ∼ 2.99 eV 和 CdI2：0.54 ∼ 3.36 eV）。发现这三种金属碘化物吸收光的波长范围为82-621 nm，