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Ab-Initio Calculations of Many body effects in electronic spectre.

Abstract : Theoretical Spectroscopy has become a field of the most active research in physics of matter. It involves using the ab initio methods to comfortably give, for example, an interpretation of experimental spectra and to predict electronic and optical properties of new materials. The state of the art for the calculation of excited states is the result of a long history. It is based on the one hand, on the theory of density functional theory (DFT) [1] and its extension to potential time-dependent (TDDFT) and, secondly, the many-body theory, one example is the famous GW approximation [2]. In this context, the purpose of this thesis was, on the one hand, to study the application of common approximations of these methods (which were developed especially for semiconductors and simple metals) in the case of systems over correlated such as the oxides of transition metals. In particular, vanadium oxide is the paradigm of these systems. It is characterized by a phase transition metal-insulator, whose physical explanation was the topic of a debate that has lasted over forty years. We showed that a GW calculation is able to reproduce without using adjustable parameters, the electron correlation effects in band structure of both phases of vanadium oxide and the satellite in the photoemission spectrum of the metal [3 ]. On the other hand, as the study of these systems requires complex calculations increasingly heavy, we have considered in this thesis an alternative approach [4]. It is based on the introduction of an effective potential, local, real and dynamic (unlike the self-energy, appearing in the GW method, which is non-local and complex) for the calculation of quasiparticle energies, which are measured in a photoemission experiment. In particular, we studied the properties of this new potential in the case of model systems and we have sought approximations for the application to real systems.
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Submitted on : Thursday, July 22, 2010 - 9:54:32 AM
Last modification on : Friday, July 31, 2020 - 9:24:06 AM
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Matteo Gatti. Ab-Initio Calculations of Many body effects in electronic spectre.. Optics [physics.optics]. Ecole Polytechnique X, 2007. English. ⟨pastel-00004109⟩

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