The pypadf package: computing the pair-angle distribution function from fluctuation scattering data

Abstract

The pair-angle distribution function (PADF) is a three- and four-atom correlation function that can characterise the local angular structure of disordered materials, particles or nanocrystalline materials. The PADF can be measured by x-ray or electron fluctuation diffraction experiments, which can be collected by scanning a small beam across a structurally disordered sample or flowing a sample across the beam path. It is a natural generalisation of the established pair-distribution methods, which do not provide angular information. This software package provides tools to calculate the PADF from from fluctuation diffraction data. The package includes tools for calculating the intensity correlation function, which is a necessary step in the PADF calculation and also the basis for other fluctuation scattering techniques.