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Single-particle modelling of X-ray Absorption and X-ray Raman Scattering spectra : from the impact of vibrations on multipole transition channels to the implementation of L2,3 edges

Abstract : This thesis work focuses on core level spectroscopies and their modelling by Quantum ESPRESSO, an open-source suite of codes. In particular this work focuses on X-Ray absorption spectroscopy (XAS), already well established, and X-Ray Raman Scattering (XRS), proving to be an increasingly popular alternative to XAS, for example under harsh experimental conditions. The first objective of this work was to study the impact of the thermal vibrations of nuclei on the multipole contributions available in XAS and XRS. Indeed, the QHA model used in this work to account for these vibration effects has been used to study light oxides before, but never to assess these effects on the secondary contribution channels of XAS (quadrupole) and XRS (monopole). The study relies on comparison between calculation and experimental data on two well-known reference compounds, rutile TiO2 and α-Al2O3. Moreover, a flaw of the QHA model when trying to reproduce subtle angular dependence signals was discovered and corrected using group theory. The second objective of the thesis was to implement calculation of XRS L2,3 edges in the XSpectra module of Quantum ESPRESSO. It was inspired by the previous implementations of XAS L2,3 edges and XRS K edges calculations in XSpectra. The monopole and dipole contributions were implemented up to the first order of the expansion of the XRS transition operator. It was tested by comparing calculation and measured data on various sulphur compounds. Good agreement with data could be produced, but was found very sensitive to the chosen core hole approximation.
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Submitted on : Wednesday, July 6, 2022 - 1:06:24 PM
Last modification on : Wednesday, August 3, 2022 - 3:53:56 AM

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  • HAL Id : tel-03715388, version 1

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Steven Delhommaye. Single-particle modelling of X-ray Absorption and X-ray Raman Scattering spectra : from the impact of vibrations on multipole transition channels to the implementation of L2,3 edges. Geochemistry. Sorbonne Université, 2022. English. ⟨NNT : 2022SORUS076⟩. ⟨tel-03715388⟩

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