Theoretical Analysis of X-Ray-Absorption spectra at the Silicon K an L2,3 Edges of Crystalline and Amorphous SiO2

In this work we present the analysis of the x-ray-absorption spectra at the silicon L2,3 and K edges in amorphous SiO2 and a quartz. This analysis consists in the comparison between experimental data and several calculations based on multiple scattering theory. An extensive discussion is presented concerning the role of the final state potential needed to reproduce the experimental data. In paticular, the effects of the cluster-size, exchange-correlation potential and the role played by self-consistent-field potential are discussed. The remarkable agreement between the theoretical computations and the experimental data allows us to identify the origin of the different features in the x-ray-absorption near-edge structure spectra.