First-principles study on the effect of high Mn doped on the band gap and absorption spectrum of ZnO

According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, we set three different concentration Mn doped ZnO models, and perform the geomertry optimizations for the three modes. The total density of states, the band structures and the optical absorption are also calculated. The results show that in the case of non-spin state, the smaller the doping concentration of Mn is, the smaller the formation energy of ZnO is and the easier the Mn doping is, thus the stabler the crystal struetuer is; the Mn doping leads to the degenerations of the impurity energy band and the conduction band, and also to the optical absorption blue-shift. These calculation results accord with the experimental results. Moreover, the magnetism exists in the system under the situation of spin polarization, the absorption spectrum has a red-shift, which is consistent with the experimental result.