MODELLING ELECTRONIC AND STRUCTURAL PROPERTIES OF QUANTUM CONFINED METAL-HALIDE PEROVSKITES

This thesis focusses on the exploration of various theoretical methods to address the interesting questions concerning electronic and optical properties of quantum-confined systems. Chapter 1 serves the purpose of providing a sufficient background for the reader on state-of-the-art knowledge and approaches in order to understand the motivations behind the study of each system: 2D layered halide perovskites (Chapter 2), lead-halide perovskite nanocrystals (Chapter 3) and metal-insulator-metal optical nanocavities (Chapter 4). In Chapter 4 the fundamentals of quantum mechanics are used to interpret the resonances of optical cavities as Epsilon-near-zero modes (ENZ), allowing us to describe them using the simple formalism of the particle in a box. In the various subparagraphs we use this approach to understand the polarization and coupling behaviours of such modes, eventually designing ENZ crystals. In Chapter 3 an analytical model is built to calculate completely ab initio the excitonic energies and the exciton binding energies of perovskite nanocrystals. This is accomplished using the state-of-the-art GW correction to the calculations of molecular orbitals energies and the Bethe-Salpeter equation for a precise evaluation of the excited states in real space. This method allows to study the effect of every physical quantity entering the description (e.g. the dielectric environment, exchange and Coulomb interactions…) on the final result, providing useful insight in the physics underlying the optical properties of these nanocrystals. In Chapter 2, Density Functional Theory is exploited to evaluate the effects of different ligands on the structural and the electronic properties of 2D halide perovskites. In the subparagraphs, various aspects are studied, for example the effects of different binding groups on the band structure, of different ligands on the Raman response and on the phase transition temperatures.