Binding energy shift (Δ B.E.) is sometimes used interchangeably with CLS. In this work, however, we refer it to the energy shift of the peak position of distinguishable components in the spectrum caused by crystal imperfections, like surface and defects, with reference to the O 2-lattice peak from the bulk part. See Scheme 1 below for a detailed computation workflow, as well as the link and difference between CLS and Δ B.E. It is noted that not all CLS lead to experimentally observable components in the spectrum. In the first instance, we studied the CLS of the non-polar (101 _ 0) surface, which is the most stable surface of ZnO. Figure illustrates the relaxed (101 _ 0) surface with different H coverage. In the slab models, each atomic layer consists of four Zn-O dimers, and two atomic layers make up a bilayer. H is only bonded to O but not Zn atoms, which has proven the more energetically favorable configuration at room temperature. The coverage of H is evaluated by the H/O atomic ratio within the topmost layer. Surface configurations with 0, 25%, 50% 100% H coverage are investigated and denoted as 0 ML, ¼ ML, ½ ML and 1ML, respectively. Figure shows the computed CLS as a function of the distance of the excited O atom to the surface. As expected, the O atoms within the surface layer have the largest shifts, which can be divided into two groups. Those directly bonded to H atoms produce a positive CLS of 2.1-2.5 eV, while the bare O atoms exhibit a negative shift of 0.06-0.49 eV. From surface to the bulk region, the magnitude of the CLS gradually diminishes and eventually converges to the bulk value. We note that it takes 7 atomic layers, or 4 bilayers for the CLS to reach convergence. Therefore, a minimum of 14 atomic layers, or 7 bilayers, are required in the surface model. Because of this, cluster models consisting of only tens of atoms cannot be expected to reliably predict the CLS in solids.