On the arrangement of sodium atoms around structural units and vibrational properties of a sodium borosilicate glass

International audienceWe have used first principles simulations in order to investigate the properties of a sodium borosilicate glass of composition 3Na2O-B2O3-6SiO2 (NBS). This composition is similar to that of the glass wool used in our daily life. The study was carried up using first principles molecular dynamics within the density functional theory framework as implemented in the VASP code [1]. In this talk, we will present the analysis of the local environments of the three building structural units of the glass network, namely silicon atoms in 4-fold coordination, and boron atoms with 3- or 4-fold coordination. We will also discuss the local distribution of the Na atoms around the basic structural units. Indeed we have identified their preferential neighborhoods and how the nature of network former and its coordination infer on the shape of these preferential regions of Na atoms. The vibrational properties have been equally studied, and the contributions of the various species have been identified. We have found that 3- and 4-fold coordinated boron atoms give rise to distinguished spectral features. Moreover, the partial vibrational density of the 3-fold coordinated B atoms has been found to be a weighted sum of 2 specific contributions so-called 3-fold symmetric coordinated B atoms and asymmetric coordinated B atoms. [1] Kresse & Hafner (1993) PRB 47, 558; Kresse & Furthmüller (1996) Comp.Mater. Sci. 6, 15; Kresse & Furthmüller (1996) PRB 54, 111