Résumé
We have carried out ab initio or combined classical and ab initio molecular dynamics (MD)simulations in order to investigate the structural and vibrational properties of several borosilicateglasses. We have considered rather simple ternary compositions with varying SiO 2 , B 2 O 3 or Na 2 Oconcentrations, or more complex compositions containing equally CaO, Al 2 O 3 or MgO. The ab initiocalculations have been carried out within the density functional theory framework as implementedin the VASP code. The classical MD simulations were carried out using different effective pairpotentials.We have studied the local structure of the various structural units, and in particular we havefocused on the structures around the boron atoms and how these are embedded into the network.We have investigated how the Na atoms are distributed around the [3] B triangles and [4] Btetrahedra. Furthermore, we have found that the Na distribution associated to a BO 4 tetrahedron isdifferent from that corresponding to a SiO 4 tetrahedron in that the former gives rise to a distributionthat is significantly more structured.The vibrational properties have been equally studied within the ab initio approach, and we haveidentified the contributions of the various species as well as those of the local structural units. Wehave also calculated the dielectric function ε(ω) as well as the absorption spectra. The latter are ingood quantitative agreement with experimental data.The results obtained in this work confirm that the atomistic simulations, in particular the ab initioones, give access to a better understanding of complex borosilicate glasses since their structuraland vibrational properties can be extracted with a good accuracy and compare very well to experimantal data.