We have carried out first-principles molecular dynamics simulations of a sodium borosilicate (NBS) glass within the framework of DFT. The composition is 6SiO2-3Na2O-B2O3 and the density was fixed to 2.51g.cm-3. The system size is 320 atoms (i.e. 60 silicon, 180 oxygen, 60 sodium and 20 boron atoms) which is rather demanding for ab-initio simulations and has been chosen to obtain a good statistics, in particular for quantities associated to the lowest concentrated element (boron). The simulations have been started at 4500K in the canonical ensemble (NVT) and followed by a simulation in the microcanonical ensemble (NVE). Subsequently, the system is progressively cooled to 300K within 60ps. In order to characterized the structure of the system we have calculated the pair correlation functions, the angular distributions, the Qn distributions, the non bridging oxygen's concentration as well as the partial structure factors. Moreover, we have studied the environment of 3- and 4-fold (BIII and BIV) coordinated boron atoms. Furthermore, the vibrational density of states has been studied in details. Indeed, both BIII and BIV atoms have specific frequencies, and the partial vibrational density of the 3-fold coordinated B atoms has been found to be a weighted sum of two specific contributions: 3-fold symmetric coordinated B (BIIIs) atoms and asymmetric coordinated B (BIIIa) atoms. Identically, the partial vibrational density of the 4-fold coordinated B atoms has been found to depend on the nature of their second neighbor namely so-called BIV(4Si-0B), BIV(3Si-1B), BIV(2Si-2B), BIV(1Si-3B), and BIV(0Si-4B) respectively with 4 Si and 0 B atoms as second neighbor and so on. The infrared spectra of our glassy models is also presented.

First-principles techniques have been employed to study the reactivity of water into a calcium aluminosilicate glass. In addition to the well known hydrolysis reactions Si-O-Si+h2O->Si-OH + Si-OH and Si-O-Al+h2O-> Si-OH+Al-OH, a peculiar mechanism is found, leading to the formation of an AlO3–H2O entity and the breaking of Al–O–Si bond. In the glass bulk,most of the hydrolysis reactions are endothermic. Only a few regular sites are found reactive (i.e. in association with an exothermic reaction), and in that case, the hydrolysis reaction leads to a decrease of the local disorder in the amorphous vitreous network. Afterwards, we suggest that ionic charge compensators transform into network modifiers when hydrolysis occurs, according to a global process firstly suggested by Burnham in 1975. Our theoretical computations provide a more general model of the first hydrolysis steps that could help to understand experimental data and water speciation in glasses.

The vibrational properties of silica glass have been intensively studied experimentally and theoretically during the last four decades. However, only few investigations have explored the evolution of the vibrational features of simple alkali glasses or silica under compression. In this contribution, we will present a detailed mode analysis of two simple (Li/Na) alkali glass models as well as for silica glass models obtained by combined classical and Car-Parrinello molecular dynamics. In particular we will discuss how the presence of the network modifier influences the relevant vibrational parameters: positions, shapes and intensities of the main peaks in the vibrational density of states (VDOS) and IR spectra. We will also show the decomposition of the VDOS on symmetry-adapted modes of the basic structural units of our models networks: SiO4 tetrahedra and SiOSi bridges.  The same analysis will be carried out in the case of few silica glass models at normal density as well as at higher density.