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Etude de petits agrégats mixtes par la méthode de la fonctionnelle de la densité et par des potentiels modèles.

Abstract : This research work has focused on the theoretical study of small mixed covalent and various iono-covalent clusters. These studies have been carried out using ab initio methods such as density functional theory (DFT) and quantum molecular dynamics, as well as analytical model potentials and global methods of potential energy surface (PES) exploration. The main purpose of the study of the covalent silicon-carbon clusters is to understand the differences between Si and C and the bond they form. The first part of the study is a systematic determination of structures and frequency vibrations of the Si–C clusters with size between 3 and 6 using DFT associated to local optimization. The second part is the global PES exploration for clusters with greater sizes and equal proportions of Si and C, for which it is almost impossible to predict the geometries using chemical intuition. This has been made using the Car and Parrinello’s method, which does not need any model potential for the system. This study has shown that this method is extremely effective, yielding numerous minima of the PES in a small number of trajectories. The second type of mixed clusters studied are lithium hydrid, sodium hydroxide and silver hydroxide clusters, which are iono-covalent clusters. The strategy is to use a model potential obtained by considering that the clusters are purely ionic in order to carry out global PES explorations using the Monte Carlo growth method, and to re-optimize the structures obtained using DFT. Results show the different perturbations caused by the covalence and by the presence of a non-spheric anionic group on the structures obtained in the three types of clusters considered. Furthermore, the calculations have enabled us to interpret experimental results on the dissociation of small mass-selected lithium hydride and silver hydroxide clusters.
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M. Bertolus. Etude de petits agrégats mixtes par la méthode de la fonctionnelle de la densité et par des potentiels modèles.. Physique Nucléaire Théorique [nucl-th]. Université PARIS XI, 1998. Français. ⟨tel-02445636⟩

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