biostudies-literatureUnknown35(4)Monacelli LCsSnI₃ is a promising ecofriendly solution for energy harvesting technologies. It exists at room temperature in either a black perovskite polymorph or a yellow 1D double-chain, which irreversibly deteriorates in the air. In this work, we unveil the relative thermodynamic stability between the two structures with a first-principles sampling of the CsSnI₃ finite-temperature phase diagram, discovering how it is driven by anomalously large quantum and anharmonic ionic fluctuations. Thanks to a comprehensive treatment of anharmonicity, the simulations deliver a remarkable agreement with known experimental data for the transition temperatures of the orthorhombic, rhombohedral, and cubic perovskite structures and the thermal expansion coefficient. We disclose how the perovskChemistry of materials : a publication of the American Chemical Society1702-1709https://www.ebi.ac.uk/biostudies/studies/S-EPMC9979598biostudies-literatureFirst-Principles Thermodynamics of CsSnI₃.PMC9979598Marzari NMonacelli LfalseFirst-Principles Thermodynamics of CsSnI₃.CsSnI₃ is a promising ecofriendly solution for energy harvesting technologies. It exists at room temperature in either a black perovskite polymorph or a yellow 1D double-chain, which irreversibly deteriorates in the air. In this work, we unveil the relative thermodynamic stability between the two structures with a first-principles sampling of the CsSnI₃ finite-temperature phase diagram, discovering how it is driven by anomalously large quantum and anharmonic ionic fluctuations. Thanks to a comprehensive treatment of anharmonicity, the simulations deliver a remarkable agreement with known experimental data for the transition temperatures of the orthorhombic, rhombohedral, and cubic perovskite structures and the thermal expansion coefficient. We disclose how the perovsk2023-01-01T00:00:00Z2023 Feb2025-05-29T16:30:18.973Z2025-04-06T03:42:06.45ZS-EPMC99795983687362510.1021/acs.chemmater.2c03475