Stability of polar ZnO surfaces studied by pair potential method and local energy density method

The polar ZnO surfaces have received wide interests due to their higher activity than the nonpolar facets in catalysis, photo-catalysis and gas sensitivity. However, the theoretical study on the relative stability of the polar ZnO surfaces is still limited. In this work, two different methods were used to calculate the surface energy of the polar ZnO(0001)–Zn and Zn(000-1)–O surfaces. The empirical pair potential method shows that the ZnO(000-1)–O terminal is more stable than the ZnO(0001)–Zn terminal because the polarizability of surface O2− is higher than that of surface Zn2+, which is in good agreement with the experimental results. However, the classic local energy density method predicts a higher stability of the ZnO(0001)–Zn terminal. The overestimation of the stability of the ZnO(0001)–Zn terminal originates from more distribution of the transferred charge to the ZnO(0001)–Zn terminal as the electron acceptor. We propose a hybrid method to fairly redistribute the contribution of the transferred charge to electron donor and electron acceptor and make the same stability trend with the experimental studies.