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Theses

Etude expérimentale et théorique des fluctuations thermiques quantiques des noyaux par spectroscopies d'absorption X et RMN

Abstract : In this thesis the impact of quantum thermal fluctuations on XANES and solid-state NMR spectra is described using an experimental and theoretical joint study. This project has two components. First, high-quality experimental data are acquired in order to observe and understand the influence of quantum vibrations in light-elements oxides. Second, a theoretical model is set up to reproduce the effects observed experimentally and describe their origin from a fundamental point of view. The developed theoretical approach is based on the density-functional theory. Within the Born-Oppenheimer and quasiharmonic approximations, the quantum thermal fluctuations of nuclei are modeled by generating atomic configurations obeying quantum statistics at finite temperature. The XANES spectra and NMR parameters are subsequently calculated in these configurations and the average results are compared with spectroscopic data at finite temperature. This approach has been validated by a joint theoretical-experimental study conducted in a series of light-element oxides, where the results were found to be in excellent agreement with the original experimental data. In addition, it is shown that the impact of the quantum fluctuations of the nuclei is influenced by the local symmetry of the probed atomic site.
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https://tel.archives-ouvertes.fr/tel-01401992
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Submitted on : Thursday, November 24, 2016 - 10:16:08 AM
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Ruidy Nemausat. Etude expérimentale et théorique des fluctuations thermiques quantiques des noyaux par spectroscopies d'absorption X et RMN. Matière Condensée [cond-mat]. Université Pierre et Marie Curie - Paris VI, 2016. Français. ⟨NNT : 2016PA066158⟩. ⟨tel-01401992⟩

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