In any case, electron delocalization over more than two atoms in PCMs has been already proved theoretically and is indeed proof of the multicenter character of the MMB. It can therefore be concluded that the unconventional MMB of PCMs and the Ah and Ai phases of group-15 and -16 elements is characterized by a blend of localized electrons between two atoms and delocalized electrons over more than two atoms. Electron delocalization is responsible for the sharing of ca. one electron (ES ≈ 1) between every two atoms in MMBs. The lower ES value in the MMBs than in covalent bonds indicates that the electronic charge shared between two atoms in MMBs is smaller than in covalent bonds. Consequently, MMBs are softer bonds than covalent bonds. The softness of MMBs has been experimentally demonstrated by the high probability of multiple events observed in laser-assisted field evaporation experiments of PCMs using atomic force microscopy , and confirmed by lattice dynamics studies . Moreover, the transformation of the strong covalent p-type bonds into the softer MMBs in group-15 and -16 elements at HP, marked by the progressive softening of the covalent bonds as atomic coordination increases at HP, accounts for the softening of the optical phonon frequencies in their covalent p-type crystalline phases at low pressures, as already proved and for the lower melting points of Bi and Po than of Sb and Te at RP and of Sb and Te than of As and Se, respectively .