Abstract
Density functional theory was employed to investigate the (111), (200), (210), (211) and (220) surfaces of CoS2. The surface energies were calculated with a sulfur environment using first-principle-based thermodynamics. It is founded that surfaces with metal atoms at their outermost layer have higher energy. The stoichiometric (220) surface terminated by two layer of sulfur atoms is most stable under the sulfur-rich condition, while the non-stoichiometric (211) surface terminated by a layer of Co atoms has the lower energy under the sulfur-poor environment. The electric structure results show that the front valence electrons of (200) surface are active, indicating that there may be some active sites on this face. There is an energy gap between the stoichiometric (220) and (211), which has low Fermi energy, indicating that their electronic structures are dynamically stable. Spin-polarized bands are calculated on the stoichiometric surfaces, and these two (200) and (210) surfaces are predicted to be noticeably spin-polarized. The Bravais–Friedel–Donnay–Harker (BFDH) method is adopted to predict crystal growth habit. The results show that the most important crystal planes for the CoS2 crystal growth are (111) and (200) planes, and the macroscopic morphology of CoS2 crystal may be spherical, cubic, octahedral, prismatic or plate-shaped, which have been verified by experiments.
Highlights
Transition metal sulfides have been widely applied in various technological areas, such as optical devices, electrical, catalytic and royalsocietypublishing.org/journal/rsos R
The stability on thermodynamic of the various terminations in the arbitrary sulfur environment was examined by surface energy
The electronic structure of five stoichiometric surfaces were calculated, and the results show that the front valence electrons of (200)-2S with the highest Fermi energy are active, indicating that there may be ‘active points’ on this surface and easy to bond with ions, molecules or crystal growth units in solution
Summary
Transition metal sulfides have been widely applied in various technological areas, such as optical devices, electrical, catalytic and royalsocietypublishing.org/journal/rsos R. Wu et al [14] predicted that the half-metallic gap might be controlled by antibonding S p rather than Co eg states by calculating the electronic band structure of CoS2 They discussed the spin bands of CoS2 (001) by experiment and computation [15]. Even though a lot of studies on surfaces of FeS2 have been reported [17,18], as we know, sulfides which crystallize in pyrite structure (FeS2, CoS2, NiS2, CuS2 and ZnS2) show great variation in electronic properties by changing transition metal ion or by substituting Se or Te in the anion site [19,20,21]. Both stoichiometric surfaces and non-stoichiometric surfaces were considered, and the variety of the sulfur chemical potential was taken into account
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