First of all, we want to stress that the basics of the transformation from pre-MMB to MMB scenarios between three atoms (A, B, and C), either by the change in pressure or composition, was initially schematized by Lee and Elliott for GST and proceeds according to the sequence from left to right displayed in Fig. . Fig. corresponds to the case of a B atom showing a strong primary covalent ppσ-bond with the A atom (both separated a short distance d1) and a weak secondary bond with the C atom (both separated a large distance d2) in which a LEP is involved. This case corresponds to d2/d1 >> 1 and we will show it is the typical case of As at RP. Fig. corresponds to the case of a B atom showing a weakened primary covalent ppσbond with the A atom and a strengthened secondary bond with the C atom. We will show that this case corresponds to d2/d1 > 1 and is the typical case of Se and Te at RP and of As above 15 GPa. Fig. corresponds to the case of a B atom showing a MMB with A and C atoms. Ideally, a fully symmetric, linear MMB, like those of the units plotted in Fig. , occurs when A and C atoms are exactly at the same distance from the B atom (d2/d1 = 1). This is the case of both phases of Polonium at RP, as already shown in the previous section.