Lead-halide perovskites are promising materials in optoelectronic devices for their unique properties including direct band gap, strong light absorption, high carrier mobility, and low fabrication cost. Here, by using ab inito molecular dynamics and electronic structure calculations, we report a systematic study on the broadening density of states (DOS) deep in the valence bands that has been experimentally observed but absent in static calculations. We quantify the broadening DOS reduction from the cubic phase to lower-temperature tetragonal and orthorhombic phases and attribute observed effects to the molecular vibrations and the anharmonicity of iodine atoms motion. Specifically, the MA cations’ vibrations are strongly linked to the moderate C–N stretch and CH₃ bend, as well as the strong CH₃ and NH₃⁺ stretches. These results present a theoretical perspective on the structural dynamics in lead-halide perovskites which may be valuable for future studies toward desired functionalities in perovskite-based optoelectronic devices.

中文翻译：

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从头算分子动力学模拟理解的CH ₃ NH ₃ PbI ₃杂化钙钛矿中态变宽的状态密度

卤化钙钛矿因其独特的性能（包括直接带隙，强光吸收，高载流子迁移率和低制造成本）而在光电器件中很有希望。在这里，通过使用从头算分子动力学和电子结构计算，我们报告了在价带深处的态加宽态密度（DOS）的系统研究，已通过实验观察到但在静态计算中不存在。我们量化了从立方相到低温四方相和正交相的不断扩大的DOS还原，并将观察到的影响归因于分子振动和碘原子运动的非谐性。特别是，MA阳离子的振动与适度的C–N拉伸和CH ₃弯曲以及强烈的CH ₃密切相关。和NH ₃ ⁺延伸。这些结果提供了关于卤化钙钛矿中结构动力学的理论观点，这对于将来对基于钙钛矿的光电器件中所需功能的研究可能是有价值的。