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:

Probing the structural, electronic and magnetic properties of multicenter Fe₂S₂⁰/⁻, Fe₃S₄⁰/⁻ and Fe₄S₄⁰/⁻ clusters. The structural, electronic and magnetic properties of neutral and anion Fe2S2, Fe3S4 and Fe4S4 have been investigated with the aid of previous photoelectron spectroscopy and density functional theory calculations. Theoretical electron detachment energies (both vertical and adiabatic) of anion clusters for the lowest energy structure were computed and compared with the experimental results to verify the ground states. The optimized structures show that the ground state structures of Fe2S2(0/-), Fe3S4(0/-) and Fe4S4(0/-) favor high spin state and are similar to their structures in proteins. The electron delocalization pattern for all the clusters and the nature of bonding between Fe and S atoms were studied by analyzing molecular orbitals. Natural population analysis demonstrates that Fe atoms act as an electron donor in all clusters, and the electron density difference map clearly shows the direction of the electron flow over the whole complex. Furthermore, the investigated magnetism shows that the Fe atoms carried most of the magnetic moments, which is due mainly to the 3d state, while only very small magnetic moments are found on S atoms.
{"Chemical": ["Fe\u2084S\u2084", "Fe2S2", "S", "Fe\u2082S\u2082", "Fe\u2083S\u2084", "Fe3S4", "Fe4S4", "Fe"]}