Significantly, the similarity of the MMBs present in sc-As and those present in the rs phase of IV-VI PCMs can be understood since both are isoelectronic (10-electron) materials . In particular, As and -GeTe show a rather close behavior because -GeTe has a layered R3m structure at RP with primary ppσ-bonds and secondary bonds similar to those of As-I. Furthermore, -GeTe undergoes a pressure-induced PT to the rs phase (-GeTe), with MMBs similar to those of As-II . It must be stressed that MMBs in As-II, as well as those in -GeTe, exhibit a hypercoordinated multicenter unit with cubic geometry as that of Fig. . In the cubic geometry, three mutually perpendicular MMBs are formed from three original primary covalent ppσ-bonds and their secondary LEP-based bonds, in a similar way as already described for crystalline chalcogenides with rs structure, such as PbS, PbSe, PbTe, β-GeTe, and GST .