Surface chemistry in a full-potential QM/MM approach: making hybrids affordable

Nanostructured oxide surfaces are promising candidates for a wide range of energy and catalysis applications. When addressing corresponding functionalities through quantitative first-principles calculations, exploitation of the localized character of the chemical processes yields numerically most efficient approaches. To this end we augment the FHI-aims\footnote{V. Blum \textit{et al.}, Comput. Phys. Commun., \textbf{180}, 2175-2196 (2009)} package with a QM/MM\footnote{N. Bernstein \textit{et al.}, Rep. Prog. Phys., \textbf{72}, 026501 (2009)} functionality, in which the nanostructure and immediate oxide surrounding is described quantum mechanically, the long-range electrostatic interactions with the support are accounted for through a polarizable monopole field, and a shell of norm-conserving pseudopotentials correctly connects the two regions. We illustrate the accuracy and efficiency of the implementation with examples from the photo-catalytic water splitting context and specifically discuss the use of charged system states to address charge transfer processes.