First Principles NMR Study of Fluorapatite under Pressure

TL;DR

This study uses density functional theory-based NMR calculations to investigate how pressure affects fluorapatite's local structure, providing insights into microscopic changes relevant for biomedical and solid-state applications.

Contribution

It presents the first ab initio NMR study of fluorapatite under pressure, correlating NMR parameters with structural changes and guiding experimental interpretation.

Findings

NMR parameters agree with experimental data

Pressure causes shrinkage of apatitic channels

NMR shielding correlates with applied pressure

Abstract

NMR is the technique of election to probe the local properties of materials. Herein we present the results of density functional theory (DFT) \textit{ab initio} calculations of the NMR parameters for fluorapatite (FAp), a calcium orthophosphate mineral belonging to the apatite family, by using the GIPAW method [Pickard and Mauri, 2001]. Understanding the local effects of pressure on apatites is particularly relevant because of their important role in many solid state and biomedical applications. Apatites are open structures, which can undergo complex anisotropic deformations, and the response of NMR can elucidate the microscopic changes induced by an applied pressure. The computed NMR parameters proved to be in good agreement with the available experimental data. The structural evaluation of the material behavior under hydrostatic pressure (from --5 to +100 kbar) indicated a shrinkage of the diameter of the apatitic channel, and a strong correlation between NMR shielding and pressure, proving the sensitivity of this technique to even small changes in the chemical environment around the nuclei. This theoretical approach allows the exploration of all the different nuclei composing the material, thus providing a very useful guidance in the interpretation of experimental results, particularly valuable for the more challenging nuclei such as $^{43}$Ca and $^{17}$O.