Graph Theory-Based Structural Analysis on Density Anomaly of Silica Glass

Understanding the structure of glassy materials is a tremendous challenge both experimentally and computationally. Despite decades of scientific research, for instance, the structural origin of the density anomaly in silica glasses is still not well understood. Atomistic simulations based on molecular dynamics (MD) produce atomically resolved structures, but extracting insights about the role of disorder in the density anomaly is challenging. Here, we quantify the topological differences between structural arrangements from MD trajectories using a graph-theoretical approach. Structural differences in silica glasses exhibiting density anomalies are captured using a graph similarity metric. To balance the accuracy and speed of the MD simulations, we utilized force matching potentials to generate the silica glass structures. This approach involves casting all-atom glass configurations as networks, and subsequently applying a graph-similarity metric (D-measure). Calculated D-measure values are then taken as the topological distances between two configurations. By measuring the topological distances of silica glass configurations across a range of temperatures, distinct structural features could be observed at temperatures higher than the fictive temperature. In addition, we compared topological distances between local atomic environments in the glass and crystalline silica phases. This approach suggests that more coesite-like and quartz-like local structures, emerge in silica glasses when the density is at a minimum during the heating process.