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Contribution à l'étude des effets à trois corps sur la structure et la thermodynamique des liquides surfondus et amorphes

Abstract : This thesis is devoted to the study of the three-body interactions on the structural and thermodynamic properties, during liquid-supercooled liquid and liquid-amorphous transformations. In this work, we use molecular dynamics simulations that gives a direct acces to the physical properties from the interactions. Therefore, both the theoretical developments and the potential can be tested by comparison with the experiment. In order to increase the accuracy of the calculations, we handled a large number of particle using a parallel version of the molecular dynamics code with a spatial decomposition of the simulation box. Our study was fisrt applied to rare gases, namely argon, krypton and xenon. The interactions between atoms, wich are dipolar in origin, are described by the Aziz and Slaman (AS) pair potential combined to the Axilrod-Teller (AT) three-body potential. It is well known that this model (AS+AT) is adapted to the study of these systems. As the AS and AT potentials cand be separated, we were able to show its influence in the liquid, supercooled and amorphous states as well as on the vitreous transition temperature Tg. In particular, the AT potential has the effect of increasing TG for all the rare gases. Thus, its use does not contradict the law of the corresponding states, wich confers an universal character on the AS+AT model for the rare gases. We also study liquid and supercooled silicon as well as liquid germanium with the Stillinger-Weber (SW) potential, wich contains both the two- and the three-body contributions. For these covalent materials, the three-body interactions are preponderant and can not be separated from the pair potential. For silicon, we have modified the SW parameter, allowing us to describe with a good accuracy the structure in supercooled states, compared with recent experiments. We were able to show that the double shoulder on the pair correlation function in this states should be accompanied by a strong increase of the density. For germanium, we have modified the parameter of the potential SW, wich controls the relative importance of the two- and three-body potentials, to obtain a good prediction of the melting point. This parameterization predicts correctly the structural properties and opens the way for a more complete study of this system
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Yasser Kadiri. Contribution à l'étude des effets à trois corps sur la structure et la thermodynamique des liquides surfondus et amorphes. Dynamique des Fluides [physics.flu-dyn]. Université Paul Verlaine - Metz, 2001. Français. ⟨NNT : 2001METZ036S⟩. ⟨tel-01775448⟩



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