Structural evolution and bond dynamics of amorphous silica under mechanical deformation using Reaxff molecular dynamics simulation

Abstract

In this work, the structural evolution and bond dynamics of amorphous silicon dioxide (a-SiO₂) under mechanical deformation under hydrostatic pressures of 100, 150, and 200 GPa are thoroughly investigated using ReaxFF reactive molecular dynamics (MD). NVT and NPT ensembles were used in simulations over five relaxation timeframes (0.15, 0.25, 0.50, 0.85, and 1.50 ps). Coordination number (CN) analysis, bond angle distributions (BAD), and radial distribution functions (RDF) were used for structural analysis. Stress-strain curves were used to evaluate mechanical response, and atomistic bond-breaking behavior and density progression were measured and visualised. The findings show that Si coordination gradually changes from being only four-fold (tetrahedral SiO₄) at ambient conditions to mostly five- and six-fold (octahedral SiO₄) environments at 200 GPa. This is accompanied by a systematic contraction of Si–O bonds from 1.62 Å to 1.50–1.55 Å, a broadening of O–Si–O bond angle distributions (FWHM: 12° → 22°), and notable increases in density (2.20 → 5.5–6.2 g/cm³). When pressure is applied, Young's modulus and fracture strength scale monotonically (E: 100–200 GPa; σf: 55–110 GPa). With implications for planetary science, shock physics, and high-pressure materials engineering, these results offer atomic-scale understanding of pressure-induced phase change in amorphous silica.