We 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, 1116

We use computer simulations to investigate the static properties of a simple glass-forming fluid in which the positions of a finite fraction of the particles have been frozen. By probing the equilibrium statistics of the overlap between independent configurations of the liquid, we find strong evidence that this random pinning induces a glass transition. At low temperatures, our numerical findings are consistent with the existence of a random first-order phase transition rounded by finite size effects.

We present a study of the structural and dynamical properties of two borosilicate glasses of compositions Na2O-B2O3-SiO2 and Na2O-CaO-B2O3-SiO2, respectively. These compositions are thus similar to the glass wool that is used in our daily life. The study was carried out using first principles molecular dynamics simulations within the DFT framework as implemented in the VASP code. The samples contained about 300 atoms, which is rather demanding for ab initio calculations, but this size is necessary to the study of the intermediate order in glasses. In particular, we have investigated how boron atoms integrate and modify the silica network, how the presence of Na and Ca atoms affects the network connectivity We also investigate the correlations between the local environments of boron and oxygen atoms, and their atomic charges extracted from electron density based population analysis methods. Furthermore we have determined the vibrational properties and identified the contributions of the different species to the density of states. We find that 3- and 4-fold coordinated boron atoms give rise to specific features in the density of states. The infrared spectra of our glassy models is also presented and directly compared to experimental data.