The bond distances in the subsurface layer was typically slightly longer, which is in line with the expected pattern of relaxations normal to the surface. The surface unit layer is expected to contract when no reconstructions are observed to account for the extra energy from the dangling bonds on the surface, while the first subsurface layer expands to counteract that. A slight contraction is sometimes observed for the second subsurface layer, however the bulk-like bonding is regained in the third subsurface layer in all slabs. Where unit layers are composed of more than four atomic layers, the bulk-like behaviour is observed within the first subsurface layer. The slab thicknesses at which the average bond lengths converged to bulk-like can be found in Table . The convergence of slab thicknesses with respect to average bond lengths is limited by the convergence of bonds lengths in bonds that are most perpendicular to the surface. This is directly related to the aforementioned contraction and expansion of the unit layers due to excess energy on the surface. In all slabs the slowest convergence was Perhaps the most striking differences in the surface and subsurface layers were seen in the ( Slabs relaxed with hybrid HSE06 functional experienced the same relaxations as with PBEsol, so a repeat description is not necessary.