Curiously, our calculated Raman frequencies for As-I soften at a much higher rate above 10 GPa than the experimental ones, i.e. the calculated Raman frequencies of As-I tend to zero at Pt, unlike the experimental ones. This means that our simulations for As, as the most extensive ones to date by Silas et al. ) show soft optical phonons that, according to the Landau theory, correspond to a second-order A7-to-Ah PT. This theoretical result contrasts with the apparent first-order character of the experimental PT . The disagreement could likely be caused by anharmonic effects that are not included in our simulations. In this context, it is well known that anharmonic effects are notable in PCMs and important for the description of the vibrational properties as the MMB formation is approached . The presence of strong anharmonic interactions in As-I close to Pt is also evidenced by the large values of the absolute phonon Grüneisen parameter, |γi|, of the A1g mode (inset of Fig. ). It must be stressed that while optical phonons in PCMs soften upon crystallization, i.e. when MMBs are formed, a hardening of the low-energy acoustic phonons is experimentally observed . The soft (hard) behavior of optical (acoustic) phonons has been also encountered in pnictogens at HP and it has been recently understood in the light of a simple model of three-center "covalentlike" interactions, which supports the multicenter character of bonds in PCMs, as already pointed out . As regards the Ah phase of As above 25 GPa (As-II), it exhibits only acoustic phonon modes (see blue line in Fig. ); however, our calculations provide non-zero optical phonon modes above 25 GPa (red line) due to the presence of a residual trigonal distortion of the sc structure, as already commented. These forbidden optical phonons of the Ah phase (also found for the Ah phases of Sb and Bi (see Fig. and S4c in ESI) and in the rs phase of PCMs ) seem to be indeed experimentally observed in As-II with a positive pressure coefficient once the MMBs are formed (see open circles in Fig. ) . The positive frequency pressure coefficient of this mode agrees with our simulations of a second-order phonon obtained as the overtone of the calculated first-order mode (see the dashed red line above 25 GPa in Fig. ). Therefore, our calculations reproduce the experimental observations and suggest that the experimental phonons in As above 25 GPa might be caused by a distortion of the sc structure in As-II, as already reported for phosphorous , likely due to an anomalously enhanced second-order Raman scattering, as recently predicted to occur in incipient metals .