A DFT and cluster expansion study of (Fe,Ni)9S8 pentlandite and unravelling doping with Mn, Co, Cu and precious metals

This study used density functional theory (DFT) adopting the universal cluster expansion (UNCLE) technique to generate different structures for (Fe,Ni)₉S₈ pentlandite and doped with Mn, Co, Cu and precious metals (Ru, Rh, Pd, Os, Ir and Pt) on the Ni and Fe tetrahedral (T) sites. The cluster expansion (CE) depicted the Fe-rich Fe₅Ni₄S₈ structure with space-group of P4₂/nmc (tetragonal) as the most stable. The doped Fe₅Ni₄S₈ structure on the Fe(T) with Mn, Cu, Rh, Pd, Ir and Pt changed from tetragonal to cubic structures, while doping with Co, Ru and Os remained tetragonal. Doping on the Ni(T) with Co, the structure changed from tetragonal to cubic, while doping with Mn, Cu, Ru, Rh, Pd, Os, Ir and Pt the structure remained tetragonal. It was found that doping with Pd on the Fe(T) generated the most thermodynamically stable compound (Fe₃Pd₂Ni₄S₈) with heats of formation of −130.24 meV. The density of states (DOS) showed that the Pd and Pt were the most preferred substitution of Fe(T) in the pentlandite structure, while the Co preferred the Ni(T) sites. In addition doping with Mn on Fe(T) and Ru doped on Ni(T) induced magnetism to the structure. This study predicted various compositions of dopants on pentlandite and laid a foundation for prediction of new mineral-compounds using DFT-CE method.