**2. Computed geometries and energies of the TiO2 surfaces in vacuum**

Recently, detailed atomic structures of the possible crystal facet terminations and their corresponding surface energies are preferably studied using a computational approach. This allows us to describe actual surface geometry and investigate how it will change in a different environment. Therefore, energetic stabilization of the specific facet might be predicted to help obtain it experimentally. However, the analyzed models are often studied in a vacuum, which enables researchers to compare the relative stability of different structures and provides a useful starting point for further investigations. Concerning TiO2 crystal planes, corresponding surface models were analyzed in detail for both anatase and rutile polymorphs, including (0 0 1), (1 0 0), (1 0 1), (1 0 3), (1 0 5), (1 1 0), and (1 1 2) structures for anatase [5–11], as well as (0 0 1), (0 1 1), (1 0 0), (1 1 0), and (1 1 1) for rutile [10–14]. On the other hand, brookite surfaces are rarely investigated. Nevertheless, a detailed study on different brookite surfaces was reported by Gong and Selloni [15], as well as additional information can be found about the (1 0 1), (1 2 1), and (2 0 1) structures [16]. Moreover, in the case of some models, different atomic geometries or possible reconstructions have been suggested. This specifically includes (1 x 4) reconstruction of the anatase
