Résumé:

We present a study of the structural and dynamical properties of liquid and glassy borosilicates of compositions Na2O-B2O3-SiO2 and Na2O-CaO-B2O3-SiO2. 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, how their coordination, as well as the oxygen speciation are affected by the temperature. 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. N.B. This work was done in collaboration with Laurent Pedesseau (L2C and INSA Rennes) and Walter Kob (L2C).