First-principles calculations of Cd _1-xZn _xS doped with alkaline earth metals for photocatalytic hydrogen generation

We have investigated the structure parameters and electronic properties of Cd _1-xZn _xS doped with alkaline earth metals by first-principles calculations on the basis of density functional theory to predict the photocatalytic activity for hydrogen generation. The optimized structure parameters show that the smaller dopants tend to pull inward their surrounding atoms and the larger ones tend to push them outward. The negative defect formation energies indicate that almost all of the doped Cd _1-xZn _xS are stable. Be or Mg doping raises the conduction band edge, and the d orbital of Ca, Sr, Ba interacts with the S _3p orbital leading to the changes of valence band. The band gap of the doped systems decreases with the increase of atomic number of dopant, and so alkaline earth metal doping acts as an effective method to adjust the optical properties.