AFLOW-SYM: platform for the complete, automatic and self-consistent symmetry analysis of crystals

Abstract

Determination of the symmetry profile of structures is a persistent challenge in materials science. Results often vary amongst standard packages, hindering autonomous materials development by requiring continuous user attention and educated guesses. This article presents a robust procedure for evaluating the complete suite of symmetry properties, featuring various representations for the point, factor and space groups, site symmetries and Wyckoff positions. The protocol determines a system-specific mapping tolerance that yields symmetry operations entirely commensurate with fundamental crystallographic principles. The self-consistent tolerance characterizes the effective spatial resolution of the reported atomic positions. The approach is compared with the most used programs and is successfully validated against the space-group information provided for over 54 000 entries in the Inorganic Crystal Structure Database (ICSD). Subsequently, a complete symmetry analysis is applied to all 1.7+ million entries of the AFLOW data repository. The AFLOW-SYM package has been implemented in, and made available for, public use through the automated ab initio framework AFLOW.

Predicting superhard materials via a machine learning informed evolutionary structure search

“…The first generation was constructed using the RANDSPG method [44], and duplicates were removed from the breeding pool via the XTALCOMP algorithm [43]. The spacegroups of the predicted superhard phases were determined using AFLOW-SYM [67], and their structures were analyzed via the tiling approach as implemented in the ToposPro package [68].…”

Parametrically constrained geometry relaxations for high-throughput materials science

“…Luckily, these parameters are already a part of the definitions used in the AFLOW Library of Crystallographic Prototypes, allowing for an easy way to define these constraints for numerous materials via their utilities [36,37]. The library sorts materials by their space group, stoichiometry, and occupied Wyckoff sites, as calculated with AFLOW-SYM [52], placing all materials that share those features into the same crystal prototype [36,37]. A reduced parameter space can then be generated from a prototype definition, and used to describe that class of materials.…”

“…By default phonopy, a very popular Python package for calculating phonon spectra with finite differences [62], uses the default spglib settings to calculate the symmetry of a material, which would misrepresent all of the tested materials using free relaxation. Commensurate phonon calculations can be achieved by performing symmetry constrained relaxations and using more robust sym- metry tools, such as AFLOW-SYM [52].…”

Metallic glasses for biodegradable implants

“…Sampling for the ternary systems ranges from 1276 to 1399 converged crystal structures. Upon removal of duplicates [72,73], structures with formation enthalpy greater than 0.05 eV, and structures for which AEs could not be determined; 399 to 580 structures remain for each system for calculation of the GFA. The predictions are shown in Fig.…”