Effects of magnesium on the structure of aluminoborosilicate glasses: NMR assessment of interatomic potentials models for molecular dynamics

Classical molecular dynamics simulations have been used to investigate the structural role of Mg and its effect when it is incorporated in sodium aluminoborosilicate glasses. The simulations have been performed using three interatomic potentials; one is based on the rigid ionic model parameterized by Wang et al. (2018) and two slightly different parameterization of the core-shell model provided by Stevensson et al. (2018) and Pedone et al. (2020) The accuracies of these models have been assessed by detailed structural analysis and comparing the simulated nuclear magnetic resonance (NMR) spectra for spin active nuclei (Si-29, Al-27, B-11, O-17, Mg-25, and Na-23) with the experimental counterparts collected in a previous work. Our simulations reveal that the core-shell parameterizations provide better structural models. In fact, they better reproduce the NMR spectra of all the investigated nuclei and give better agreement with known experimental data. Magnesium is found to be five coordinated on average with distances with oxygen in between a network modifier (like Na) and an intermediate network formed (like Al). It prefers to lay closer to three-coordinated B atoms, forming B-NBO bonds, with respect to Si and especially Al. This can explain the formation of AlO5 and AlO6 units in the investigated Na-free glass, together with a Si clusterization.