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Propriétés structurales et spectroscopiques des agrégats d'hydrocarbures aromatiques polycycliques

Léo Dontot 1
1 MAD - Modélisation, Agrégats, Dynamique (LCPQ)
LCPQ - Laboratoire de Chimie et Physique Quantiques
Abstract : Modeling of neutral or cationic molecular clusters remains a challenge in ab initio approaches as soon as the molecules involved are large or when their number exceed several units. We develop, in this thesis, a mixed method based on the combination of the DFTB method, an approximation of the Density Functional Theory (DFT), with a Configuration Interaction (CI). This method (DFTB-CI) provides an original and efficient approach to obtain a correct description of the charge resonance within cationic clusters. The application to polycyclic aromatic hydrocarbons clusters is of interest in various fields such as physics and chemistry of the interstellar medium, chemistry of the atmosphere and also combustion processes. This work has enabled the description of structural properties of the ground state of neutral and cationic clusters of pyrene and coronene containing up to ten molecules. A multi-method strategy has been implemented in order to efficient search for the most stable structures with the global exploration algorithm “Parallel Tempering Monte Carlo”. In addition to the structural properties, we have determined the quantities characterizing the stability of these clusters (binding and dissociation energies) as well as their electronic properties such as the dependency of the ionization potentials on the size in good agreement with experimental results. Finally, we propose an extension to the DFTB-CI model in order to compute the excited states of molecular clusters. The results on dimers are found in good agreement with ab initio calculations. An application to small cationic clusters of benzene and pyrene presents the determination of their electronic absorption spectra.
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Léo Dontot. Propriétés structurales et spectroscopiques des agrégats d'hydrocarbures aromatiques polycycliques. Physique [physics]. Université de Toulouse 3 Paul Sabatier, 2014. Français. ⟨NNT : 2014TOU30341⟩. ⟨tel-02863600⟩

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