Abstract

Defects in thin oxide films on metal substrates affect metal work function and determine the chemical and physical properties of an oxide. However, accurately predicting properties of these heterogeneous systems is still challenging. Here we use a new approach to treat a mixed metal/metal oxide system within density functional theory, which is based on the application of the auxiliary density matrix method (J. Chem. Theory Comput.2010, 6, 2348) to calculate the exchange interaction at a sharp interface between the two materials, as implemented in the CP2K code. This method is used to calculate the shift of the Ag work function in the MgO/Ag(001) system as a function of the MgO film morphology as well as charge state, position, and density of oxygen vacancies. An accurate band alignment between metal and oxide allows us to predict the relative stabilities of different charge states of oxygen vacancies in MgO as a function of their position with respect to the interface with Ag. Our results confirm that F+ centers are the most stable defects at terrace sites of MgO clusters and show that F0 and F+ centers can have comparable energies at low-coordinated sites, such as steps and corners. They show how thin oxide film roughness as well as oxygen deficiency can affect the metal work function. © Published 2013 by the American Chemical Society.