Ring-originated anisotropy of local structural ordering in amorphous and crystalline silicon dioxide

Rings comprising chemically bonded atoms are essential topological motifs for the structural ordering of network-forming materials. Quantification of such larger motifs beyond short-range pair correlation is essential for understanding the linkages between the orderings and macroscopic behaviors. Here, we propose two quantitative analysis methods based on rings. The first method quantifies rings by two geometric indicators: roundness and roughness. These indicators reveal the linkages between highly symmetric rings and crystal symmetry in silica and that the structure of amorphous silica mainly consists of distorted rings. The second method quantifies a spatial correlation function that describes three-dimensional atomic densities around rings. A comparative analysis among the functions for different degrees of ring symmetries reveals that symmetric rings contribute to the local structural order in amorphous silica. Another analysis of amorphous models with different orderings reveals anisotropy of the local structural ordering around rings; this contributes to building the intermediate-range ordering. Quantification of large topological motifs is important for understanding chemical linkages between structural ordering and macroscopic behaviors. Here, two quantitative analysis methods based on rings are proposed to reveal information on orders and linkages in crystalline and amorphous materials.

Automated summary

Rings composed of chemically bonded atoms are important topological motifs for ordering of network-forming materials. In this article, two quantitative analysis methods based on rings are proposed to reveal information on ordering and linkages in crystalline and amorphous materials.