Multiple scattering calculations of the XANES Si K-edge in amorphous silica

X-ray absorption spectra in the near-edge region (XANES) contain information about the structural organization of materials over distances up to about 10 إ. In glasses, the structural information over such a large distance is rather complex and difficult to obtain. One possible method for extracting this information is to use multiple scattering (MS) calculations in real space to mimic X-ray absorption spectra in the XANES region. Such calculations for disordered systems require that a good structural model be assumed. We present full MS calculations at the silicon K-edge of amorphous silica, performed using atomic co-ordinates taken from molecular dynamics (MD) calculations. The spectra corresponding to several clusters are averaged in order to account for the disorder. The experimental spectrum is well reproduced by the calculations, showing the validity of the combination of MD and MS calculations. The results show an influence of medium-range order up to more than 5 إ. Two different structural models taken from ab initio and classical MD are compared for this study.