Abstract In this study, the elastic, electronic, and optical properties of cubic, tetragonal and monoclinic K2TeX6 (X = Cl, Br, I) perovskite derivatives are investigated using first-principles calculations. The results reveal that different space groups have a minor influence while the atomic number of X has a significant influence on the physical properties of these perovskite derivatives. In their crystal structures, X and K atoms form X–K ionic bond, while X and Te atoms form X–Te ionic bond with more covalent components. For K2TeBr6 perovskite derivatives within the three different space groups, the close Br–Te bond lengths slightly decrease as the symmetry decreases. However, for the monoclinic K2TeX6 (X = Cl, Br, I) perovskite derivatives, as the atomic radius of X increases, the X–Te bond lengths increase with the decrease in covalent bond components. All the K2TeX6 (X = Cl, Br, I) perovskite derivatives exhibit obvious elastic anisotropy. The monoclinic K2Te2I6 perovskite derivative is brittle, but K2TeX6 (X = Cl, Br) perovskite derivatives are ductile. In the electronic structures of the perovskite derivatives, the top valence bands are primarily contributed by X-p (Cl-3p, Br-4p, or I-5p) and Te-5s orbits, and the bottom conduction bands are dominated by Te-6p orbit. The effective masses and carrier mobilities exhibit distinct anisotropy due to the anisotropic crystal structures. As the atomic number of X increases, the effective masses of electrons and holes gradually decrease, while the carrier mobilities increase. Especially, the higher carrier mobilities of monoclinic K2Te2I6 perovskite derivative are caused by its smaller effective masses. The K2TeX6 (X = Cl, Br, I) perovskite derivatives exhibit excellent dielectric functions and absorption coefficients in the visible and ultraviolet regions.

中文翻译：

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使用密度泛函理论的 K2TeX6 (X=Cl, Br, I) 钙钛矿衍生物的机械、电子和光学特性

摘要 在这项研究中，使用第一性原理计算研究了立方、四方和单斜 K2TeX6 (X = Cl, Br, I) 钙钛矿衍生物的弹性、电子和光学性质。结果表明，不同空间群的影响较小，而 X 的原子序数对这些钙钛矿衍生物的物理性质有显着影响。在它们的晶体结构中，X和K原子形成X-K离子键，而X和Te原子与更多的共价成分形成X-Te离子键。对于三个不同空间群内的 K2TeBr6 钙钛矿衍生物，随着对称性的降低，紧密的 Br-Te 键长略有降低。然而，对于单斜 K2TeX6 (X = Cl, Br, I) 钙钛矿衍生物，随着 X 原子半径的增加，X-Te 键长随着共价键组分的减少而增加。所有 K2TeX6 (X = Cl, Br, I) 钙钛矿衍生物都表现出明显的弹性各向异性。单斜 K2Te2I6 钙钛矿衍生物较脆，但 K2TeX6 (X = Cl, Br) 钙钛矿衍生物具有延展性。在钙钛矿衍生物的电子结构中，顶部价带主要由 Xp（Cl-3p、Br-4p 或 I-5p）和 Te-5s 轨道贡献，底部导带由 Te-6p 轨道主导. 由于各向异性晶体结构，有效质量和载流子迁移率表现出明显的各向异性。随着X原子序数的增加，电子和空穴的有效质量逐渐减少，而载流子迁移率增加。尤其，单斜 K2Te2I6 钙钛矿衍生物较高的载流子迁移率是由其较小的有效质量引起的。K2TeX6 (X = Cl, Br, I) 钙钛矿衍生物在可见光和紫外区表现出优异的介电函数和吸收系数。