Carnevali Virginia, Agosta Lorenzo, Slama Vladislav, Lempesis Nikolaos, Vezzosi Andrea, Rothlisberger Ursula
Laboratory of Computational Chemistry and Biochemistry, Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
Department of Chemistry, University of Ioannina, Ioannina, Greece.
Nat Commun. 2025 Jul 24;16(1):6825. doi: 10.1038/s41467-025-61351-7.
Formamidinium-lead-iodide (FAPbI) has a rich phase diagram, and long-range correlation between the organic cations and lattice dipoles can influence phase transitions and optoelectronic properties. System size effects are crucial for an appropriate theoretical description of FAPbI. We perform a systematic ab initio study on the structural and electronic properties of the photoactive phase of FAPbI as a function of system size. To ensure an accurate theoretical description, three criteria must be satisfied: the (correct) value of the band gap, the extent (or the absence of) structural distortions, and the zeroing out of the total dipole moment. The net dipole moment vanishes as the system size increases due to PbI octahedra distortions rather than due to FA rotations. Additionally, thermal band gap fluctuations are predominantly correlated with octahedral tilting. The optimal agreement between simulation results and experimental properties for FAPbI is only achieved by system sizes approaching the nanoscale.
甲脒碘化铅（FAPbI）具有丰富的相图，有机阳离子与晶格偶极子之间的长程相关性会影响相变和光电特性。系统尺寸效应对于FAPbI的适当理论描述至关重要。我们对FAPbI光活性相的结构和电子性质作为系统尺寸的函数进行了系统的从头算研究。为确保准确的理论描述，必须满足三个标准：带隙的（正确）值、结构畸变的程度（或不存在）以及总偶极矩归零。由于PbI八面体畸变而非FA旋转，净偶极矩随着系统尺寸的增加而消失。此外，热带隙波动主要与八面体倾斜相关。FAPbI的模拟结果与实验性质之间的最佳一致性仅在系统尺寸接近纳米尺度时才能实现。
