Percolation criticality of amorphous-amorphous transitions in compressed glasses

The low-to-high-density transition in compressed silica glass is investigated using percolation theory. Large-scale molecular dynamics simulations of SiO$_2$ glasses, with system sizes of up to 10$^6$ atoms and pressures ranging from 0 to 35 GPa, were carried out to investigate the emergence of structural motifs and their growth to system-spanning length scales under compression. On this basis, we introduced long-range descriptors that complement conventional local and medium-range structural measures. The results reveal critical percolation transitions of SiO$_Z$-SiO$_Z$ clusters with increasing coordination number $Z$. The critical exponents slightly deviate from the standard (random) correlation, a behavior that seems to be more pronounced for higher coordinated polyhedra than for tetrahedra, suggesting a possible rigidity percolation mechanism. SiSi$_z$-SiSi$_z$ clusters were also analyzed using the non-bonded approach. Bonded and non-bonded approaches complement each other in a particularly illuminating way for describing pressure-induced structural transformations and common mechanisms shared by bonded glasses, such as SiO$_2$, and non-bonded glasses, such as amorphous ice.