Ab initio modelling of multicomponent borosilicate glasses
Résumé
We have carried out 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 experimental data.