Validating First Principles Molecular Dynamics Calculations of Solid/Liquid Interfaces with X-ray Reflectivity

The interface between a metal oxide electrode and liquid water plays a crucial role in energy conversion processes such as photo-electrochemical water splitting and CO$_{\mathrm{2}}$~reduction to create fuel from sunlight.~ First principles electronic structure calculations are useful tools to obtain electronic properties relevant to catalysis, such as electron energy alignment between the electrode surface and a reacting molecule, but~their ability to predict realistic structural models requires careful validation. We combine calculations of interfacial X-ray structure factors [1] from~ab-initio molecular dynamics trajectories with experimental X-ray reflectivity measurements [2] to obtain a validation protocol~for structural models of aqueous interfaces. Simultaneously, we provide a means to interpret X-ray reflectivity measurements without the need for~model-dependent empirical fitting, offering unique insight into the influence of atomic-scale structure upon reaction mechanisms at surfaces.~We will discuss in particular the case of the water/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ (001) interface [3]. [1] M. Plaza et al, \textit{JACS }\textbf{138}, 4 (2016) [2] J. G. Catalano, \textit{Geochimica et Cosmochimica Acta} \textbf{75}, 10 (2011) [3] P. Huang et al, \textit{J Phys. Chem. C} \textbf{118}, 8 (2014).