The most important point in Fig. is that three distinct stages occur in As between 0 and 35 GPa. These three stages correspond to stages 1 to 3 in Fig. . In stage 1 (up to 16 GPa), there is a weak (strong) decrease of d1 (d2) as well as a correspondingly small (large) increase of ρd1 (ρd2). In stage 2 (from 16 to 25 GPa), there is a decrease of d2 and an anomalous increase of d1 as well as a corresponding decrease (increase) of ρd1 (ρd2). Finally, once both primary and secondary bonds equalize (above 25 GPa) the Ah phase corresponding to stage 3 is reached. This stage is characterized by linear MMBs that show the normal decrease of the bond distance and increase of the bond charge density as pressure increases. A clearer picture of the three stages along the A7-to-Ah PT in As can be noted by the S-like behavior of d1 vs. d2 and ρd1 vs. ρd2 in As-I (see Fig. ), since d2 (ρd2) always decreases (increases) with increasing pressure.