Faujasite is one of the most industrially employed zeolite for its catalytic properties. The strong Brønsted bulk bridging AlÀ OHÀ Si sites are often thought to be the main origin of the Brønsted acidity of faujasite. However, many reactions also take place at the surface of the material and of its mesopores, where other types of acid sites exist. This study aims at unraveling the nature and strength of faujasite bulk and surface acid sites. Using Density Functional Theory (DFT), we rank the faujasite acid sites based on their stability, investigate their dehydration properties, and study their Brønsted and Lewis acidity via the adsorption of pyridine. Calculations are performed on cells with high (47 for bulk cells and about 300 for surface slabs) and low Si/Al ratio (about 3) and on cells containing defects under the form of silanol nests. These environments generate Brønsted acid sites of various strengths, and strong Lewis acid sites, even in the absence of extra-framework species.

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The inclusion of sophisticated density-dependent electronic stopping and electron-phonon coupling calculated with first-principles methods into molecular dynamics simulations of collision cascades has recently become possible thanks to the development of the so-called EPH (for Electron-PHonon) model. This work aims at employing the EPH model in molecular dynamics simulations of collision cascades in Si. In this context, the electronic stopping power is investigated in Si at low energies with Ehrenfest Dynamics calculations. Also, the parametrization of the EPH model for Si, from firstprinciples Ehrenfest Dynamics simulations to actual molecular dynamics simulations of collision cascades, is performed and detailed. We demonstrate that the EPH model is able to reproduce very closely the density-dependent features of the energy lost to electrons obtained with ab initio calculations. Molecular dynamics collision cascade simulations results obtained in Si using the EPH model and the simpler but widely employed Two Temperature Model (TTM) are compared, showing important discrepancies in the collision cascades results obtained depending on the model employed.

Primary interaction simulations with neutrons are performed on Si1-xGex alloys with a Monte-Carlo (MC) code using the Binary Collision Approximation (BCA). Then, a statistical study of the collisions cascades development in Si0.8Ge0.2, Si0.7Ge0.3 and Si0.5Ge0.

The sensitivity of collision cascades simulations to the Two-Temperature Model main parameters is investigated by performing an extensive statistical study both in Si and Ge materials. The purpose is to identify the parameters of the Two-Temperature Model whose impact is the most significant on the cascades properties and to discuss the physical role of each parameter. We demonstrate that the electronic stopping power and electron phonon coupling have a drastic impact both in Si and Ge but that these two parameters act differently on those two materials due to their distinct thermal properties. We show that the formation of thermal spikes and therefore of amorphous pockets is sensitive to the electronic specific heat. The effects are again very distinct in Si and in Ge. The influence of both the threshold velocity for the stopping power and the electron-phonon coupling activation time are found to be negligible at the considered energies.