Crystallisation of liquid silica under compression: a molecular dynamics simulation

Abstract

In this study, we employ molecular dynamics simulations to develop a large model (19,998 atoms) of liquid SiO₂ at 3500 K. We construct models at different pressures in the 0–100 GPa range using the Beest–Kramer–Santen (BKS) potential and periodic boundary conditions. The goal is to detail the structural transition from the polyamorphic liquid state of SiO₂ to the crystalline stishovite form, which occurs between 45 and 60 GPa. We analyse the polyamorphic state of liquid SiO₂ by examining the formation of SiO_x clusters from 2 to 60 GPa. Beyond 60 GPa, the pair radial distribution functions (PRDFs) for Si–O, O–O and Si–Si display multiple peaks, indicating the crystalline phase. This observation is further supported by examining the bond angle distribution, the fraction of SiO_x units and OSi_x linkages, Si–O bond lengths within SiO_x units, structural visualisations and the analysis of ring statistics in the liquid SiO₂ system, all of which underscore the comprehensive changes in the structure of the system.