Fig. 3

DFT model for water adsorption on cleaved Ca₃Ru₂O₇. a Top view DFT model of the pristine surface (Ca—blue, O—red, H—white, Ru—yellow). The unit cell is marked by the rectangle. The distances from the bridge sites B1 to B4 to the surface oxygen atoms O1 and O2 differ because of the tilted RuO₆ octahedra and are listed in Table 1. The distance B1-O1 is shown as an example, other distances are constructed analogously. b Top view and c side view of the DFT model of the most preferred configuration B1O1 for one dissociated water monomer with E _{ads_B1O1} = 1.64 eV. The first subsurface layer of RuO₆ octahedra is shown. Water dissociates, forming an (OH)_ads group adsorbed on Ca-Ca bridge site B1 with a H transferred to the neighboring surface oxygen atom, O1. The tilt angle of the hydroxylated RuO₆ octahedron increases from 12.9° to 16.3°, when compared to the pristine surface. The energetically equivalent configuration B2O2 is not shown. d According to Tersoff-Hamann simulations, STM shows the (OH)_ads as a bright feature. When compared to the Ca-Ca bridge centre (dashed line), the (OH)_ads sits slightly closer to the O_surfH (in [100] direction)