Sub-Monolayer Water Adsorption on Alkaline Earth Metal Oxide Surfaces: A First-Principles Study

In the present work, we predict atomic structures of adsorbed complexes that should appear on alkaline earth metal oxide (001) terraces in thermodynamic equilibrium with water and oxygen gases. Density-functional theory with the hybrid exchange-correlation functional HSE06 combined with the self-consistent many-body dispersion approach [1] is used to calculate total energies. The choice of this functional is validated by renormalized second-order perturbation theory [2]. An unbiased search for global minima of H$_x$O$_y$ adsorption is performed using first-principles genetic algorithm for periodic models. $x$ and $y$ as a function of temperature and pressure are determined using {\em ab initio} atomistic thermodynamics. We find a range of H$_2$O chemical potentials where one-dimensional adsorbed water structures are thermodynamically stable on CaO(001). On MgO(001) and SrO(001), such structures are not found. The formation of the one-dimensional structures is explained by the balance between water-water and water-surface interactions.\\[4pt] [1] A. Tkatchenko, R. A. DiStasio, Jr., R. Car and M. Scheffler, Phys. Rev. Lett. \textbf{108}, 236402 (2012);\\[0pt] [2] X. Ren, P. Rinke, G. E. Scuseria, M. Scheffler, Phys. Rev. B \textbf{88}, 035120, (2013).