Methylammonium lead iodide, as related organometal halide perovskites, emerged recently as a particularly attractive material for photovoltaic applications. The origin of its appealing properties is sometimes assigned to its potential ferroelectric character, which remains however a topic of intense debate. Here, we rationalize from first-principles calculations how the spatial arrangement of methylammonium polar molecules is progressively constrained by the subtle interplay between their tendency to bond with the inorganic framework and the appearance of iodine octahedra rotations inherent to the perovskite structure. The disordered tetragonal phase observed at room temperature is paraelectric. We show that it should a priori become ferroelectric but that iodine octahedra rotations drive the system toward an antipolar orthorhombic ground state, making it a missed ferroelectric.

甲基铵碘化铅作为相关的有机金属卤化物钙钛矿，最近成为光伏应用中特别有吸引力的材料。其吸引人的特性的起源有时归因于其潜在的铁电特性，但这仍然是一个激烈争论的话题。在这里，我们从第一性原理计算中合理化甲基铵极性分子的空间排列如何逐渐受到它们与无机骨架结合的趋势和钙钛矿结构固有的碘八面体旋转出现之间的微妙相互作用的限制。在室温下观察到的无序四方相是顺电的。我们证明它应该先验地变成铁电体，但是碘八面体旋转将系统推向反极性正交基态，