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Impurities such as iron (Fe), copper (Cu) and manganese (Mn) are often present in sphalerite (ZnS) mineral. These impurities significantly influence the properties of ZnS. This study investigated the effect of Cu, Fe and Mn content on the structural properties of the bulk and surface structures of ZnS using density functional theory with dispersion correction and Hubbard U (DFT-D+U). This method is implemented in the Vienna Ab-initio Simulation Package (VASP) code. The computed bulk properties of pure ZnS (lattice parameters (a) = 5.397 Å and band gap (Eg) = 2.013 eV) were in good agreement with the reported value of a = 5.400 Å and Eg = 2.078 eV. For the doped systems, the lattice parameters and band gap values were found to be Zn0.6Cu0.4S (a = 5.309 Å, Eg = 2.00 eV), Zn0.5Fe0.5S (a = 5.155 Å, Eg = 0.0 eV) and Zn0.8Mn0.2S (a = 5.338 Å, Eg = 0.0 eV) which were all lower than those of pure ZnS. The computed surface energies of the ideal ZnS and doped ZnS were ZnS (110) surface (0.82 J/m2), which was higher than the surface energies of the doped surfaces of Zn0.6Cu0.4S (0.78 J/m2) and Zn0.8Mn0.2S (0.44 J/m2), but lower than that of Zn0.5Fe0.5S (1.68 J/m2). This suggested that the doping of ZnS bulk with the Fe underestimate the investigated properties, while doping ZnS (110) surface with Cu and Mn enhance the surface stability.
Keywords: VASP code; Surface energies; lattice parameters; band gap; DFT-D+U ZnS (110)
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