全无机卤族钙钛矿光电性能优异但存在光致相分离等稳定性问题。由于亚稳相实验困难，第一原理计算是重要的稳定性研究手段。但现有计算大都未重视其弱键合强极性的化学本质而忽略非谐效应和化学序影响、且受限计算成本，导致数据不准且有限。本项目研究一个典型体系Cs(Sn,Pb)(Br,I)3的本征稳定性。针对数据不准问题，提出非谐效应和化学序显著影响稳定性的假说，基于非谐效应和集团展开计算方法学的最新进展检验此假说，针对性地设计合理计算方案，继而准确计算重要成分点的热力学数据。针对数据有限问题，使用相图计算（CALPHAD）方法拟合和外推第一原理计算及实验数据，构建各体系的全成分空间热力学模型，并计算多组元多相温度-成分相图。最终，基于准确且充足数据，分析重要稳定性问题的热力学机理并建议可能解决方案。该工作有望为开发弱键合强极性半导体合金成为性能优异且稳定可用的功能材料提供重要理论指导和代表性研究案例。

All-inorganic halide perovskites possess excellent optoelectronic properties but are subject to stability issues. Due to difficulty in experimenting on metastable phases, first-principles calculations are important means to study their stability. However, most past calculations did not consider anharmonic effects or treat chemical ordering explicitly, not appreciating their weakly-bonded and strongly-polar chemical nature, were limited by computing cost, and produced inaccurate and insufficient data. This project will study the intrinsic stability of a prototypical pseudo-quaternary alloy system Cs(Sn,Pb)(Br,I)3. To address the problem of data inaccuracy, this project hypothesizes that anharmonicity and chemical long-/short-range order are both significant, and will firstly test the hypothesis quantitatively based on latest developments in the computational methodology for anharmonic free energy predictions and cluster expansion, design a computational scheme accordingly that balances predictive accuracy and computing cost, and calculate thermodynamic data for stable phases at important compositions following the scheme. To address the problem of data insufficiency, this project will employ the CALPHAD approach to extrapolate the first-principles computational and experimental data, develop thermodynamic models covering the full composition range for all components of the system, and calculate their multicomponent multiphase phase diagrams. Finally, this project will analyze, based on accurate and sufficient data, the thermodynamic mechanisms for major stability problems and propose possible solutions. This research may provide theoretical guidance and an exemplary research case for developing stable and high-performance functional materials based on weakly-bonded and strongly-polar semiconductor alloys.