Effect of oxygen vacancy and zinc interstitial on the spontaneous polarization of wurtzite ZnO: Maximally localized Wannier functions analysis

First-principles calculations are employed to obtain the maximally localized Wannier functions of wurtzite ZnO with O vacancy and Zn interstitial. Through analyzing the shape of Wannier functions and the distribution of Wannier function centers, the influence of O vacancy and Zn interstitial in different charge states on the spontaneous polarization are investigated. We found that polarization appears in \bar{1}010 and [\bar{1}2\bar{1}0] orientations when the defects are charged, and the absolute polarization value will get larger as the defect charge state increases. Neutral O vacancy decreases the spontaneous polarization along the [0 0 0 1] direction. For O vacancy in +1 and +2 charge states, an additional electronic field is introduced, and it results in a dramatic change in the electronic structure, which reverses the polarization. However, in the case of Zn interstitial in +2 charge state, we find that it is the ionic relaxation that plays a dominant role in the polarization reversal.