Extended Data Fig. 6: Calculated ideal 1 × 1 surfaces and superstructures with different S_OH.

a, b, Ideal 1 × 1 phase with S_OH = 8 and S_OH = 15, respectively. c, d, \(\sqrt{19}\times \sqrt{19}\) phase with S_OH = 2 and S_OH = 9, respectively. e, f, \(2\sqrt{19}\times \sqrt{19}\) phase with S_OH = 2 and S_OH = 9, respectively. The black lines indicate the areas used to determine the total number of nearest-neighbor dangling OH pairs. S_OH describes the total number of nearest-neighbor dangling OH pairs within an area equivalent to the unit cell of \(\sqrt{19}\times \sqrt{19}\) phase. For \(2\sqrt{19}\times \sqrt{19}\) phase, since its unit cell area is twice as large as that of \(\sqrt{19}\times \sqrt{19}\) phase, the obtained S_OH should be divided by 2. The orange and yellow triangles represent tetrahedron structures in different stacking types. H and O atoms of the lower-lying water molecules in the topmost bilayer are denoted as white, and dark blue spheres, respectively. O atoms of H-up and O-up water molecules are denoted as red and yellow spheres, respectively. Bilayers below the surface are shown in light blue.