Quantifying the Structure of Disordered Materials

TL;DR

This paper introduces a new framework for analyzing disordered materials' structure by developing a generalized distance function, GIIP, which captures local atomic environments and reveals structural trends in glasses.

Contribution

It presents the GIIP distance, a novel method for characterizing disordered materials' structure based on low-dimensional atomic environment manifolds.

Findings

GIIP effectively captures local atomic environments.

Slower quenching increases local tetrahedral symmetry.

Descriptors reveal structural trends in glasses.

Abstract

Durable interest in developing a framework for the detailed structure of glassy materials has produced numerous structural descriptors that trade off between general applicability and interpretability. However, none approach the combination of simplicity and wide-ranging predictive power of the lattice-grain-defect framework for crystalline materials. Working from the hypothesis that the local atomic environments of a glassy material are constrained by enthalpy minimization to a low-dimensional manifold in atomic coordinate space, we develop a novel generalized distance function, the Gaussian Integral Inner Product (GIIP) distance, in connection with agglomerative clustering and diffusion maps, to parameterize that manifold. Applying this approach to a two-dimensional model crystal and a three-dimensional binary model metallic glass results in parameters interpretable as coordination number, composition, volumetric strain, and local symmetry. In particular, we show that a more slowly quenched glass has a higher degree of local tetrahedral symmetry at the expense of cyclic symmetry. While these descriptors require post-hoc interpretation, they minimize bias rooted in crystalline materials science and illuminate a range of structural trends that might otherwise be missed.