Atomistic modelling of complex borosilicate glasses
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 borosilicate
glasses. We have considered rather simple ternary compositions with varying SiO 2 , B 2 O 3 or Na 2 O
concentrations, or more complex compositions containing equally CaO, Al 2 O 3 or MgO. The ab initio
calculations have been carried out within the density functional theory framework as implemented
in the VASP code. The classical MD simulations were carried out using different effective pair
potentials.
We have studied the local structure of the various structural units, and in particular we have
focused 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] B
tetrahedra. Furthermore, we have found that the Na distribution associated to a BO 4 tetrahedron is
different from that corresponding to a SiO 4 tetrahedron in that the former gives rise to a distribution
that is 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 of the local structural units. We
have also calculated the dielectric function ε(ω) as well as the absorption spectra. The latter are in
good quantitative agreement with experimental data.
The results obtained in this work confirm that the atomistic simulations, in particular the ab initio
ones, give access to a better understanding of complex borosilicate glasses since their structural
and vibrational properties can be extracted with a good accuracy and compare very well to experimantal data.