Julien Perradin | Searcharxiv

arXiv2026

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.

cond-mat.dis-nn↗

arXiv2026

Nexus-CAT: A Computational Framework to Define Long-Range Structural Descriptors in Glassy Materials from Percolation Theory

Nexus-CAT (Cluster Analysis Toolkit) is an open-source Python package for cluster detection and percolation analysis of atomistic simulation trajectories. Standard structural tools, such as the pair distribution function or structure factor, fail to capture the long-range connectivity changes underlying amorphous-amorphous transitions in glassy materials. Nexus-CAT addresses this gap by reading extended XYZ trajectory files and identifying clusters via a Union-Find algorithm with path-compression. Four clustering strategies, i.e., distance-based, bonding, coordination-filtered, and shared-neighbor, are implemented through a Strategy Factory design pattern, enabling the treatment of diverse network topologies. The program computes key percolation properties with percolation detection based on a rigorous period vector algorithm. The package is validated against theoretical predictions and applied to glasses with different bonding environments, namely vitreous silica, vitreous ice, and amorphous silicon. One original result is the observation of a percolation transition prior to crystallization in the latter, indicating that pressure-induced crystallization is initially driven by an amorphous transformation with similar coordination number. The code is also designed to be readily extended to gels, cements, and other disordered materials. Nexus-CAT is fully available on GitHub and PyPI.

cond-mat.dis-nn↗