6. The formation of EDMBs with increasing electronic density proceeds in a gradual, similar way in both group-15 and -16 elements. This result is in line with previous suggestions that proposed the formation of multicenter bonds by the increase in mass density, e.g. by increasing pressure . Notably, we have shown that the mechanism of EDMB formation proceeds via different stages that depend on the type of LEP involved in the secondary bonds. In group-16 elements (with a p-type LEP involved in secondary bonds), the mechanism of EDMB formation comprises two stages, while in group-15 elements (with an s-type LEP involved in secondary bonds the mechanism comprises three stages. We suggest that these mechanisms could be universal, at least, in p-type elements, and that all materials undergoing a bonding change from a covalent ppσ-bond plus a secondary bond to an EDMB upon increase of electronic density will follow a two-or three-stages mechanism depending on the type of LEP involved in secondary bonds. In particular, we predict that EDMB formation in group-17 elements (Br and I) will proceed via a two-stage mechanism due to the p-type LEPs present in these elements at RP. In more complex compounds, such as IV-VI and V2-VI3 compounds, the presence of two or three phases must be further clarified. We have also shown that these stages show a parallelism with the molecular, semimolecular, and atomic/polymeric stages in nitrogen and hydrogen at HP. 7. The formation of MMBs in group-15 and -16 elements either at RP or at HP is in good agreement with the 2D map showing the number of electrons shared (ES) vs. the normalized number of electrons transferred (ET) used by Wuttig and coworkers to classify bonds in materials . By calculating the ES and ET values of different materials with MMBs, either ERMBs or EDMBs, we have shown that these two multicenter bonds are located in different positions of the map, so the ES and ET values calculated with QTAIM theory seem to be valid to explain the different types of bonds in materials (in particular group-15 and -16 elements) that occur under compression and upon change of composition.