Representational Analysis of Extended Disorder in Atomistic Ensembles Derived from Total Scattering Data

TL;DR

This paper introduces a symmetry-based representational analysis method to interpret atomistic ensembles from total scattering data, improving understanding of medium-range order and disorder in complex crystalline materials.

Contribution

It presents a novel approach using representational analysis to extract meaningful displacement modes from RMC ensembles, enhancing interpretation of disorder and symmetry breaking.

Findings

Enables robust characterization of medium-range order.

Provides symmetry-adapted displacement modes.

Improves understanding of disorder in complex crystals.

Abstract

With the increased availability of high intensity time-of-flight neutron and synchrotron X-ray scattering sources that can access wide ranges of momentum transfer, the pair distribution function method has become a standard analysis technique for studying disorder of local coordination spheres and at intermediate atomic separations. In some cases, rational modeling of the total scattering data (Bragg and diffuse) becomes intractable with least-squares approaches and necessitates reverse Monte Carlo (RMC) simulations using large supercells. However, the extraction of meaningful information from the resulting atomistic ensembles is challenging, especially at intermediate length scales. We use representational analysis to describe displacements of atoms in RMC ensembles from an ideal crystallographic structure. Rewriting the displacements in terms of a local basis that is descriptive of the ideal crystallographic symmetry provides a robust approach to characterizing medium-range order (and disorder) and symmetry breaking in complex and disordered crystalline materials. This method enables the extraction of statistically relevant displacement modes (orientation, amplitude, and distribution) of the crystalline disorder and provides directly meaningful information in a symmetry-adapted basis set that is most descriptive of the crystal chemistry and physics.