Regarding Sb and Bi, our simulations also confirm the presence of the three stages of the mechanism of MMB formation along the A7-to-Ah PT (Fig. , S5, and S12b-c in ESI). In particular, Sb-I is in stage 1 at 0 GPa and in stage 2 above 3.5 GPa, whereas stage 3 should occur experimentally in Sb-II above 8 GPa. On the other hand, Bi-I is in stage 1 (close to stage 2) at 0 GPa and in stage 2 (close to stage 3) in Bi-II at 2.5 GPa. Since the Ah phase has not been experimentally reported in Bi, stage 3 should occur experimentally in Bi-III above 2.7 GPa, as already pointed out in the previous section. Interestingly, our results obtained for Bi are consistent with the comments of Häussermann et al. , who stated that the electronic band structure of Bi-III shows a Fermi level located in a valley in the bands formed by bonding and antibonding p-orbitals with a "significant covalent bonding contribution". They also noted that the "covalent bonding contribution" in Bi-III is no longer present in the A2 phase of group-15 elements that occurs at higher pressures, where a full electron delocalization is found, as expected in metallic bonding. In this context, we consider that the term "significant covalent bonding contribution" should be now understood as the MMB contribution in Bi-III because MMBs are also directional, like covalent bonds, and unlike metallic bonds. Finally, we have to stress that a progressive decrease of the pressure range of stages 1 and 2 is observed on going from As (stage 1: 0 -15 GPa; stage 2: 15 -25 GPa) to Sb (stage 1: 0 -3.5 GPa; stage 2: 3.5 -7 GPa) and Bi (stage 1: 0 -2.5 GPa; stage 2: 2.5 -2.7 GPa).