Quantification of local geometry and local symmetry in models of disordered materials

Journal article

We suggest two metrics for assessing the quality of atomistic configurations of disordered materials, both of which are based on quantifying the orientational distribution of neighbours around each atom in the configuration. The first metric is that of geometric invariance: i.e., the extent to which the neighbour arrangements are as similar as possible for different atoms, allowing for variations in frame of reference. The second metric concerns the degree of local symmetry. We propose that for a set of configurations with equivalent pair correlations, ranking highly those configurations with low geometric invariance but with high local symmetry selects for structural simplicity in a way that does not rely on formal group theoretical language (and hence long-range periodic order). We show that these metrics rank a range of SiO2 and a-Si configurations in an intuitive manner, and are also significantly more sensitive to unphysical features of those configurations in a way that metrics based on pair correlations are not. We also report that implementation of the metrics within a reverse Monte Carlo (RMC) algorithm gives rise to an energy landscape that is too coarse (at least in this initial implementation) for amorphous structure 'solution'. Cliffe and Goodwin suggest two metrics for assessing the quality of configurations of disordered materials: namely, local geometric invariance and degree of local symmetry. These enable screening for structural simplicity in a way that does not rely on formal group theoretical language (and hence long-range periodic order). The authors show that various SiO2 and a-Si configurations are ranked sensibly by this approach, which is found to be significantly more sensitive to unphysical features than pairwise correlations. © 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Authors: Cliffe, M; Goodwin, A

• Publication status: Published
• Journal: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
• Volume: 250
• Issue: 5
• Pages: 949-956
• Publication date: 2013-05-01
• DOI: 10.1002/pssb.201248553
• EISSN: 1521-3951
• ISSN: 0370-1972
• Language: English
• Keywords: reverse Monte Carlo; disordered materials; pair distribution function; local symmetry