The structure of sodium trisilicate glass via molecular dynamics employing three-body potentials

Molecular dynamics simulations (MD) employing multibody potentials were used to simulate sodium trisilicate glass (Na₂O.3SiO₂). A multibody term has been added to a pair potential in order to incorporate the bond directionality which is expected for the partially covalent silicate structure. The structure of the glass was analyzed and results were compared to those found using two-body potentials and molecular statics, as well as to experimental results found using x-ray diffraction, XPS, NMR, and EXAFS. Current results compared favorably to experiment and showed improvement over results obtained using two-body potentials. Nearest neighbor distances and coordination numbers agreed well with published data. Although two-body potentials normally show overcoordinated silicon (>4.3) and broad O-Si-O tetrahedral angle distributions, in this study all silicon exhibited tetrahedral coordination (4.0) and the O-Si-O bond angle distribution was markedly sharpened. The number of nonbridging oxygens was shown to be nearly equal to the number of sodium ions present, and a reasonable distribution of Qi species was found. The overall structure closely resembled the modified network structure of glass proposed experimentally, with silicon tetrahedra remaining intact and sodium ions breaking up the network through the creation of nonbridging oxygens.