Résumé
We have carried out combined classical and ab initio molecular dynamics (MD)simulations in order to investigate the structural and vibrational properties of severalborosilicate glasses. We have considered rather simple ternary compositions withvarying SiO 2 , B 2 O 3 or Na 2 O concentrations, or more complex compositionscontaining equally CaO, Al 2 O 3 or MgO. The ab initio calculations have been carriedout within the density functional theory framework as implemented in the VASPcode. The classical MD simulations were carried out using different effective pairpotentials.We have studied the local structure of the various structural units, and inparticular we have focused on the structures around the boron atoms and how theseare embedded into the network. We have investigated how the Na atoms aredistributed around the [3] B triangles and [4] B tetrahedra. Furthermore, we have foundthat the Na distribution associated to a BO 4 tetrahedron is different from thatcorresponding to a SiO 4 tetrahedron in that the former gives rise to a distribution thatis significantly more structured.The vibrational properties have been equally studied within the ab initio approach,and we have identified the contributions of the various species as well as those ofthe local structural units. We have also calculated the dielectric function ε(ω) as wellas the absorption spectra. The latter are in good quantitative agreement withexperimental data. The results obtained in this work confirm that the atomisticsimulations, in particular the ab initio ones, give access to a better understanding ofcomplex borosilicate glasses since their structural and vibrational properties can beextracted with a good accuracy and compare very well to experimental data.