Molecular dynamics calculations for boron oxide and sodium borate glasses

Molecular dynamics (MD) calculations were carried out for boron oxide and sodium borate glasses using the interionic potentials derived by the MD calculations of crystals. It is shown that the calculated composition dependence of the fraction of the boron ions having tetrahedral coordination is in good agreement with the results measured by NMR. The pair distributions and bond angle distributions around 3- and 4-fold coordinated boron ions showed remarkable differences from each other and gave the particular local structures. It is concluded that the network is developed at first with an increase of Na₂O content and the maximum development is shown near 33 mol% Na₂O. Above 33 mol% Na₂O, the network of the sodium borate glass starts to disintegrate and a significant increase of the non-bridging oxygen ion is found.