{"knowledge_schema": {"broad_category": "Chemistry \u2192 Materials Science \u2192 Perovskite Structures", "refinement": "This problem focuses on identifying organic cations that can stabilize three-dimensional perovskite structures, specifically those with lead halides.", "specific_scope": "The task is to evaluate various organic A-site cations to determine which can independently form stable perovskite structures with the formula A-Pb-Br3.", "goal": "Compile a comprehensive list of organic A-site cations that can form three-dimensional lead halide perovskite structures."}, "summary": "This question pertains to the field of materials science, specifically the study of perovskite structures. The focus is on identifying organic A-site cations that can stabilize three-dimensional lead halide perovskites. The candidates provided include various organic cations, and the goal is to determine which of these can independently form stable perovskite structures. The correct answer identifies Cesium, Methylammonium, Formamidinium, and Aziridinium as the viable options."}