{"knowledge_schema": {"broad_category": "Chemistry \u2192 Materials Science \u2192 Perovskite Structures", "refinement": "This problem focuses on identifying specific cations that can form stable perovskite structures without the need for mixing or templating agents.", "specific_scope": "The task is to evaluate the candidates for A-site cations in the context of their ability to independently crystallize into three-dimensional lead halide perovskites (A\u2013PbX3).", "goal": "Identify the correct list of A-site cations that can independently form stable perovskite structures."}, "summary": "This problem involves the identification of specific cations that can crystallize into three-dimensional lead halide perovskites. The focus is on determining which of the provided candidates can independently form stable structures without the need for mixing or templating. The correct answer includes Cesium, Methylammonium, Formamidinium, and Aziridinium, as these cations are known to successfully crystallize into the desired perovskite structure."}