At this point, it is worth pointing out that MMBs (with ES ≈ 1) are an intermediate step between covalent bonds (with ES ≈ 2) and metallic bonds (with ES → 0), as shown by arrows in Fig. . This means that MMBs feature an almost equal mixture of localized and delocalized electrons. Since pressure tends to increase atomic coordination, the octahedral coordination will be surpassed at high enough pressures and there will be an increase in the number of delocalized electrons relative to localized electrons. This means that the MMB will tend to become a metallic bond at HP, as suggested by Wuttig and coworkers . The tendency of materials with p-type bonds to change from covalent bonds towards MMBs and finally to metallic bonds upon the change of pressure or composition is indicated with arrows for pure covalent and ionocovalent p-type materials in Fig. . It can be speculated that the fully metallic bond will occur in pnictogens and chalcogens as well as in IV-VI and V2-VI3 chalcogens when the eightfold-coordinated bodycentered cubic (bcc, Strukturberich type A2) phase is reached, since the A2 phase is a common HP phase to all of them . This hypothesis seems to agree with the results of Häuserman and coworkers , who commented (later discussed) the notable differences between the electronic band structure and DOS in the A2 HP phase and previous phases at lower pressures in Bi. However, the hypothesis of metallic bonding in the bcc phase is contrary to the claim of Lubchenko and coworkers, who consider that this phase is still characterized by multicenter bonds . Further work in this direction must be done that is outside the scope of the present manuscript. As already pointed out, a recent paper has suggested that the ES vs. ET map should not be used to understand the origin of MMBs in PCMs , because it is impossible to locate in this map materials with more than a single type of bond. This is true and that is why Wuttig et al. only locate materials through their principal bond. We consider that even though the ES vs. ET map cannot be used to univocally characterize materials, it is valid to characterize bonds in materials. We propose that the ES vs. ET map is equivalent to the map already published by Mori-Sánchez et al. to classify bonding types with two parameters, the electron density flatness, f, and the global charge-transfer index, c, which has been suggested to be equivalent to the van Arkel-Ketelaar diagram . According to our calculations, As-II and -Po (with sc structures) and PbS (with rs structure) show f values close to 0.1, i.e. intermediate between those of materials with covalent bonding, like Ge and GaAs, and materials with metallic bonding, such as Al and Cu. These results indicate that the region of metavalency, intermediate between covalent and metallic regions, can be also placed in the f vs. c map, and correspondingly in the equivalent van Arkel-Ketelaar diagram. All in all, this means that the ES vs. ET map seems to be equivalent to the f vs. c map of Mori-Sánchez et al. and the classic van Arkel-Ketelaar diagram. Thus, our results confirm Wuttig's claims that the ES magnitude is valid for locating the metavalency region between the covalent and metallic regions . It must be mentioned that these results differ from those of Lubchenko and coworkers, who suggest that the multicenter bond is only intermediate between ionic and metallic bonds . On the other hand, our results confirm the claim of Lubchenko and coworkers that multicenter bonds are promoted with increasing density since the changes in pressure and in composition (going down within a group) allow for increasing the electronic density of the material.