Contribution of molecular dynamics simulations and ab initio calculations to the interpretation of Mg K-edge experimental XANES in K2O-MgO-3SiO2 glass

The structural environment of Mg in a K-bearing silicate glass of composition K2MgSi3O8 is investigated by x-ray absorption near-edge structure (XANES) spectroscopy at the Mg K-edge. XANES calculations are performed using a plane-wave electronic structure code, and a structural model obtained by classical molecular dynamics coupled to ab initio relaxation. Bond valence theory is used to validate plausible environments within the structural models. Comparison between the experimental and calculated spectra enables us to conclude that the Mg atoms are located in distorted tetrahedral sites. Site distortions are found to be correlated to the theoretical shift of the XANES edge position.