To revisit the weakly bonded d 0 systems, we start by COHP analysis for corundum, rutile and pentoxide systems at the bulk and surface levels (Figure ). Unlike our previous studies, that focused solely on the ICOHP of a single bond (between a metal-oxide in a bulk or at the surface), here instead we consider the ICOHP sum of all the nearest covalent M-O bonds (<2.5 Å) around the active site. Please note that bonds longer than 2.5 Å are treated as non-covalent, therefore adding zero to ICOHP. For example, in an octahedral system, this approach incorporates the sum of all four equatorial and two axial bonds around the active site, as depicted in Figure . The amount of local bonds is then adjusted structures other types of coordination such as, tetrahedral, square-pyramidal, square planar, etc.) To facilitate comparisons across various oxidation states, we simply use normalized ICOHP values 2 , by dividing the sum of ICOHP of nearest bonds by the oxidation state of the metal in the bulk of a respective system (i.e. 4 for MO2). Next, Figures Changing the group number from 3d to 4d to 5d changes the values slightly to more negative, suggesting that later TMOs form stronger (and shorter) covalent bonds. For completeness, pentoxide system is featured in both the high (Figure ) and the low coverage (see Figure ) surfaces.