Density functional theory was used to investigate the electrostatic effect of various oxygen impurities at the interface of MgO/Ag, including interstitial oxygen defects, substitutional oxygen defects, and reconstructed substitutional oxygen defects. When interstitial and reconstructed substitutional oxygen impurities were generated at the interface, an additional bond with the film was formed and the work function of the interface increased. On the other hand, in the case of substitutional oxygen generated at the interface, the oxygen impurities migrated into the Ag subinterface layer and the work function of the interface was slightly decreased. It can be inferred that the origin of the work function change is the dipole moment induced by oxygen impurities. The results of this study indicate that the work function of MgO/Ag (001) can be finely tuned with interfacial oxygen impurities. (C) 2012 Elsevier B.V. All rights reserved.