You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Energies and Spin States of FeS(0/-) , FeS2 (0/-) , Fe2 S2 (0/-) , Fe3 S4 (0/-) , and Fe4 S4 (0/-) Clusters. The structures and energies of the electronic ground states of the FeS(0/-) , FeS2 (0/-) , Fe2 S2 (0/-) , Fe3 S4 (0/-) , and Fe4 S4 (0/-) neutral and anionic clusters have been computed systematically with nine computational methods in combination with seven basis sets. The computed adiabatic electronic affinities (AEA) have been compared with available experimental data. Most reasonable agreements between theory and experiment have been found for both hybrid B3LYP and B3PW91 functionals in conjugation with 6-311+G* and QZVP basis sets. Detailed comparisons between the available experimental and computed AEA data at the B3LYP/6-311+G* level identified the electronic ground state of (5) Δ for FeS, (4) Δ for FeS(-) , (5) B2 for FeS2 , (6) A1 for FeS2 (-) , (1) A1 for Fe2 S2 , (8) A' for Fe2 S2 (-) , (5) A'' for Fe3 S4 , (6) A'' for Fe3 S4 (-) , (1) A1 for Fe4 S4 , and (1) A2 for Fe4 S4 (-) . In addition, Fe2 S2 , Fe3 S4 , Fe3 S4 (-) , Fe4 S4 , and Fe4 S4 (-) are antiferromagnetic at the B3LYP/6-311+G* level. The magnetic properties are discussed on the basis of natural bond orbital analysis.
{"Chemical": ["FeS2", "Fe3 S4", "Fe3 S4 (-)", "FeS(-)", "Fe4 S4 (-)", "FeS", "Fe4 S4", "Fe2 S2", "Fe2 S2 (-)", "FeS2 (-)"]}