First-principles study of the structural and electronic properties of CoX0.25S1.75 (X = F, Cl, or Br)

In this study, the structural and electronic properties of CoX0.25S1.75 (X = F, Cl, or Br) were investigated based on spin-polarized first-principles calculations. S-F, S-Cl, and S-Br covalent bonds are not present in CoX0.25S1.75 (X = F, CI, or Br). The generalized gradient approximation (GGA) + U and Heyd-Scuseria-Ernzerhof hybrid functional method may overestimate the spin-down band gap for CoS2. The results obtained for CoX0.25S1.75 (X = F, Cl, or Br) using the GGA method are expected to be more reasonable. Only the half-metal CoX0.25S1.75 can be used for spintronic applications and the metal (X = Cl or Br) is more suitable for use in supercapacitors. The p-d hybridization between S and Co CoX0.25S1.75 atoms in CoF0.25S1.75 is stronger compared with that in CoS2. The p-d hybridization between S(S-X) and Co atoms is stronger whereas that between S(S-S) and Co atoms is weaker in CoX0.25S1.75 (X = Cl or Br). Doping with F and Cl (Br) atoms in CoS2 induces new bands with less and more dispersion, respectively. In CoX0.25S1.75 (X = F or CI), X atoms gain more electrons than S atoms and the charge density difference indicates that S atoms donate electrons to F and Cl atoms. However, in CoBr0.25S1.75, Br atoms gain fewer electrons than S atoms and there is almost no charge transfer between S and Br atoms.