Ab initio density functional theory of Fe5Ni4S8 (022) and (400) surfaces

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In the present study we used density functional theory (DFT) to study compare stability of Fe5Ni4S8 (022) and (400) surfaces by investigating their structural and electronic properties. Structural optimization for possible terminations of both (022) and (400) surfaces were performed. There were six different possible terminations in the case of the (022) surface, with two being non-dipolar and 3 terminations for (400). These slab surfaces were obtained by cleaving the optimized bulk Fe5Ni4S8 structures. Slabs were separated from replicas repeating by a vacuum width of 20 Å. Different terminations were tested and only considered the non- dipole surfaces. The calculated surface energy of (022) was less than that of (400), which suggested that (022) surface was the most stable surface, and thus the pentlandite (Pn) mineral is likely to cleave through (022) surfaces during crushing. The EF fell into the pseudo gap for both surfaces suggesting electronic stability. The electron charge density showed high charge density centred on Ni atoms more than on the Fe atoms, predicting more charge transfer from Ni atoms to S atoms.