Calculation on surface energy and electronic properties of CoS2

Density functional theory was employed to investigate the (111), (200), (210), (211), and (220) surfaces of CoS2. The surface energy were calculated with a sulfur environment using first-principles based thermodynamics. It is founded that surfaces with metal atoms at their outermost layer are predicted to have higher energy. The stoichiometric (220) surface terminated by two layer of sulfur atoms is the most stable under the sulfur-rich condition, while the nonstoichiometric (211) surface terminated by a layer of Co atoms has the lower energy under the decreasingly sulfur-poor environment. A spin-polarized bands were calculated on the stoichiometric surfaces. The electric structure results showed that there may be some active sites on (200) since it has high Fermi energy and its front valence electrons are active. There was an energy gap between the stoichiometric (220) and (211), which have low Fermi energy, indicating that the electronic structures were dynamically stable. These two stoichiometric (200) and (210) surfaces are predicted to be noticeably spin-polarized. The results of BFDH method was adopted to predict crystal growth habit. It showed that the important crystal planes for the CoS2 crystal growth were (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.