Orientational Effects in the Low Pair Continuum of Aluminium

TL;DR

This study compares theoretical predictions of aluminium's dynamic structure factor using TDDFT with high-resolution x-ray measurements, highlighting the importance of orientation effects and lattice considerations in modeling polycrystalline materials.

Contribution

It demonstrates that TDDFT can accurately reproduce experimental spectra when orientation averaging and lattice effects are properly included.

Findings

TDDFT predicts strong anisotropy in the DSF of aluminium.

Experimental data can resolve orientation dependencies in polycrystalline aluminium.

Accounting for lattice effects improves the agreement between theory and experiment.

Abstract

We compare the predictions of the dynamic structure factor (DSF) of ambient polycrystalline aluminium from time-dependent density functional theory (TDDFT) in the pair continuum regime to recent ultrahigh resolution x-ray Thomson scattering measurements, collected at the European XFEL. TDDFT predicts strong anisotropy in the DSF at the wavenumber examined here, even with $q$-blurring accounted for. The experimental spectrum has more than sufficient resolution and signal-to-noise levels to resolve these orientation dependencies, and therefore the orientational averaging of the polycrystalline sample is observed rigorously. Once the orientation averaging is accounted for, TDDFT is able to reproduce the experimental spectrum adequately. Finally, comparisons of predicted DSFs from jellium to experiment demonstrates the importance of accounting for lattice effects in modelling the spectrum from a polycrystal.