DFT computation of Cu adsorption on the S atoms of sphalerite (1 1 0) surface

The adsorption of Cu2+ ion on the various S atoms at sphalerite (1 1 0) surface was simulated using the density functional theory (DFT). The results of DFT indicate that Cu2+ ion can be readily adsorbed on the S atom of sphalerite (1 1 0) surface, i.e., Cu adsorption on the top site of S atom (top adsorption) and on the bridge site between two S atoms (bridge adsorption). The calculated adsorption energies for the top and bridge adsorptions of Cu2+ ion are −657.24 kJ/mol and −670.11 kJ/mol, respectively. The density of states (DOSs) analysis shows that a peak of Cu 3d orbital near to the Fermi level is formed after Cu2+ ion adsorption. The formed Cu 3d orbital peak and the S 3p orbital peak are overlapped between −2.00 eV and 0 eV, implying a steady chemical adsorption. Mulliken population analysis shows that the Cu atom was reduced with the resulting oxidation of the S and Zn atoms during the Cu adsorption process. A comparison of DOS between the Cu2+ ion adsorption and the Cu substitution for the top site Zn atom shows that the DOS of Cu2+ ion adsorption is very similar to that of Cu substitution. Thus, it was concluded that the adsorption of Cu2+ ion on the S atom of sphalerite surface can also result in the activation of sphalerite.