Pressure-Driven Lattice Stiffening and Thermodynamic Stability in Hybrid Lead Halide Perovskites: A Unified DFT–EOS–Machine Learning Study

Hybrid organic–inorganic lead halide perovskites are promising materials for optoelectronic and photovoltaic systems, but there is limited evidence of their mechanical and thermodynamic stability under external pressure. The current work is a comparative, systematic investigation of the structures, elasticities, and thermophysical properties of MAPbI 3 , MAPbBr 3 , FAPbI 3 , and FAPbBr 3 under pressure within a combined density functional theory, equation-of-state, and machine-learning approach. Energy–volume relations can be used to derive equilibrium factors, including the equilibrium volume, the bulk modulus, and its pressure derivative. Elastic constants, bulk and shear moduli, Debye temperature, volume thermal expansion coefficient, and Gruneisen parameter are compared in a pressure range from 0 to 15 GPa. Smooth elastic compression is observed for all compounds and no pressure-induced phase transition occurs, confirming mechanical stability over the range studied. The perovskites based on bromide appear to have better stiffness and lower compressibility as compared with iodide-based perovskites, and FA-based ones have superior lattice flexibility as compared to MA-based ones. The excellent numerical agreement among DFT, EOS, and ML predictions shows the strength of the computational strategy. The pressure-dependent trends calculated by us give some fundamental insights into lattice stiffening, anharmonicity suppression, and thermodynamic stabilization, and offer some practical strategy designs for strain-tolerant and pressureresilient perovskite optoelectronic devices