From symmetry to stability: structural and electronic transformation in Cs₂KInI₆

Cs2KInI6 is a promising lead-free halide double perovskite with a calculated direct band gap of 1.94 eV, ideal for solar cell applications. Our first-principles calculations reveal that its cubic phase (Fm3̅m) is dynamically unstable. Using an accelerated machine learning approach, we identify 42 dynamically stable structures and further validate these findings using first-principles calculations on 11 of these. The most stable phase has Cmc21 symmetry with 20 atoms/unit cell. It lies 13 meV/atom above the convex hull but lacks octahedral cation coordination. The most stable perovskite-like structure has P3̅ symmetry with 10 atoms/unit cell and low octahedral connectivity. Structure-property trade-offs are highlighted, with calculated distortions generally widening the band gap, shifting it from direct to indirect, and flattening the band edges. This work showcases the synergy of genetic algorithms, machine-learned potentials, and first principles validation for discovering stable, complex materials. This archive contains all our input, output files, the data and scripts.

Cs₂KInI₆是一种极具应用前景的无铅卤化物双钙钛矿，经计算其直接带隙（direct band gap）为1.94 eV，适配太阳能电池应用场景。我们的第一性原理（first-principles）计算结果显示，其立方相（空间群Fmoverline{3}m）存在动力学不稳定性。通过加速机器学习方法，我们筛选得到42个动力学稳定结构，并对其中11个结构开展第一性原理计算以验证上述发现。稳定性最高的相具有Cmc2₁空间群对称性，晶胞内包含20个原子，其能量较凸包（convex hull）高13 meV/atom，但不存在八面体阳离子配位结构。稳定性最优的类钙钛矿结构具有Poverline{3}空间群对称性，晶胞内包含10个原子，且八面体连接性较低。本研究凸显了结构与性能之间的权衡关系：计算结果表明，结构畸变通常会加宽带隙，使带隙从直接带隙转变为间接带隙，并使能带边趋于平坦。本工作展示了遗传算法、机器学习势函数与第一性原理验证三者的协同应用，可用于发现稳定的复杂材料。本数据集归档包含所有输入文件、输出文件、相关数据与脚本。