Finite Temperature Effects on the X-ray Absorption Spectra of Crystalline Aluminas from First Principles

TL;DR

This study demonstrates that including phonon-assisted transitions in first-principles calculations accurately reproduces finite-temperature X-ray absorption spectra of aluminas, revealing temperature-dependent spectral features absent at static lattice levels.

Contribution

The paper introduces a method to incorporate phonon effects into DFT calculations of XAS, enabling realistic finite-temperature spectral predictions for crystalline materials.

Findings

300 K XAS reproduces pre-edge peak in α-Al₂O₃

Correctly describes two of three peaks in γ-Al₂O₃ at 300 K

Second peak arises from 1s to mixed s-p transitions, absent at 0 K

Abstract

By including phonon-assisted transitions within plane-wave DFT methods for calculating the X-ray absorption spectrum (XAS) we obtain the Al K-edge XAS at 300 K for two Al$_2$O$_3$ phases. The 300 K XAS reproduces the pre-edge peak for $\alpha$-Al$_2$O$_3$, which is not visible at the static-lattice level of approximation. The 300 K XAS for $\gamma$-Al$_2$O$_3$ correctly describes two out of the three experimental peaks. We show that the second peak arises from 1s to mixed $s$-$p$ transitions and is absent in the 0 K XAS. This letter serves as a basis for future applications, as the method is generalizable to any atom and edge.