  The surfaces of most metals immersed in aqueous electrolytes have a
several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the
existence of both metal|oxide and oxide|liquid electrotlyte interfaces, and
makes it challenging to correlate atomic length-scale structures with
electrochemical properties such the potential-of-zero-charge (PZC). The PZC
value has been shown to be correlated the pitting onset potential for
corrosion. In this work, we conduct large-scale Density Functional Theory and
ab initio molecular dynamics to calculate the PZC of a
Al(111)|gamma-Al(2)O(3)(110)|water double-interface model within the context of
aluminum corrosion. By partitioning the multiple interfaces involved into
binary components with additive contributions to the overall work function and
voltage, we predict the PZC to be -1.53 V vs. SHE for this model. We also
calculate the orbital energy levels of defects like oxygen vacancies in the
oxide, which are critical parameters in theories associated with pitting
corrosion. We predict that the Fermi level at the PZC lies above the impurity
defect levels of the oxygen vacancies, which are therefore uncharged at the
PZC. From the PZC estimate, we predict the voltage needed to create oxygen
vacancies with net positive charges within a flat-band approximation.
