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Density functional theory modelling of electric double layers at oxide/electrolyte interfaces

Most solid oxides, metal or main group, are sufficiently ionic to act as amphoteric acids when interfaced with aqueous solution. The oxide surface will acquire a negative charge at high pH due to deprotonation of adsorbed water or hydroxide groups and a positive charge at low pH due to protonation of exposed oxygen ions. The surface charge is compensated in an electrical double layer (EDL) by accumulation of counter ions from the aqueous solution. Atomistic modelling of EDL’s is a challenge in particular for the periodic supercell models used in Density Functional Theory (DFT) electronic structure calculation. A key property of EDL’s is the capacitance, which is of interest in colloid and earth science and heterogeneous catalysis. We have developed a method based on the application of finite electric fields which allows us to compute the capacitance of a periodic model of an EDL at fixed composition (which is crucial in DFT calculations). The proposed project consists of application of this method to common oxides such as silicates and aluminates and their (partially or fully) hydroxylated and hydrated forms. The main computational workhorse is the CP2K DFT molecular dynamics package.