Multiple scattering calculations of the XANES SiK-edge in amorphous silica

X-ray absorption spectra in the near-edge region (XANES) contain informatio n about the structural organization of materials over distances up to about 10 Angstrom. In glasses, the structural information over Such a large dist ance is rather complex and difficult to obtain, One possible method for ext racting this information is to use multiple scattering (MS) calculations in real space to mimic X-ray absorption spectra in the XANES region. Such cal culations for disordered systems require that a good structural model be as sumed. We present full NIS 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 average d in order to account for the disorder. The experimental spectrum is well r eproduced by the calculations, showing the validity of the combination of M D and MS Calculations. The results show an influence of medium-range order up to more than 5 Angstrom. Two different structural models taken from ab i nitio and classical MD are compared for this study. (C) 2001 Elsevier Scien ce B.V. All rights reserved.