A quantum perturbative pair distribution for determining interatomic potentials from extended X-ray absorption spectroscopy

TL;DR

This paper presents a quantum perturbative method to extract interatomic potentials from single-shell EXAFS spectra, enabling analysis of lattice anharmonicities with validated sensitivity tools.

Contribution

It introduces a novel quantum perturbative pair distribution function approach for fitting interatomic potentials directly from EXAFS data, incorporating a fourth-order Taylor expansion.

Findings

Successfully applied to AgI at 77 K, determining Ag–I potential parameters.

Achieved good agreement with previous studies on interatomic potentials.

Provided a statistical F-test tool for assessing sensitivity to lattice anharmonicities.

Abstract

In this paper we develop a technique for determining interatomic potentials in materials in the quantum regime from single--shell Extended X-ray Absorption Spectroscopy (EXAFS) spectra. We introduce a pair distribution function, based on ordinary quantum time--independent perturbation theory. In the proposed scheme, the model potential parameters enter the distribution through a fourth--order Taylor expansion of the potential, and are directly refined in the fit of the model signal to the experimental spectrum. We discuss in general the validity of our theoretical framework, namely the quantum regime and perturbative treatment, and work out a simple tool for monitoring the sensitivity of our theory in determining lattice anharmonicities based on the statistical $F$--test. As an example, we apply our formalism to an EXAFS spectrum at the Ag K--edge of AgI at T=77 K. We determine the Ag--I potential parameters and find good agreement with previous studies.