New interaction potentials for alkali and alkaline-earth aluminosilicate glasses

Abstract

We apply a recently developed optimization scheme to obtain effective potentials for alkali and alkaline-earth aluminosilicate glasses that contains lithium, sodium, potassium, or calcium as modifiers. As input data for the optimization, we used the radial distribution functions of the liquid at high temperature generated by means of ab initio molecular dynamics simulations and density and elastic modulus of glass at room temperature from experiments. The new interaction potentials are able to reproduce reliably the structure and various mechanical and vibrational properties over a wide range of compositions for binary silicates. We have tested these potentials for various ternary systems and find that they are transferable and can be mixed, thus allowing to reproduce and predict the structure and properties of multi-component glasses.

New interaction potentials for borate glasses with mixed network formers

“…The method described above is justified based on a previous observation that mechanical properties have a strong dependence on the interaction potential and different potentials can predict very similar structures even if the predicted elastic moduli differ significantly 38 . Even though there is no change in the topology of the structure during the optimization since we don't re-melt, the improved interaction parameters result in improved properties as was shown in our previous work on aluminosilciates 27 and will be shown in this paper. It is also important to note here that the iterative process we described above already produces samples that have decent coordination and since we do not re-melt the samples, changes in the average coordination tend to be small during the optimization.…”

“…The superscript "ref" refers to the first principles or experimental reference data towards which the optimization was carried out, and superscript "calc" refers to the calculated properties using the current parameter set. The major difference in the cost function from our previous work on aluminosilicates 27 is the inclusion of the average boron coordination. It is very important to note here that unlike previous work in literature 16,18,22 we do not include the experimental trends in the composition in our cost function or have system specific or composition dependent parameters to reproduce experimental results.…”

“…and , { , , , , , , } O Si Li Na K Al B    . All the parameters from our previous work 27,28 were maintained constant and oxygen charge was evaluated for each compositions in order to maintain charge neutrality by using a similar scheme as described previously 27,34 . The short-range interactions were cut off at 8 Å while the Coulombic interactions were cut off at 10 Å.…”

“…For the various binary borate glasses, we used 0.2X2O-0.8B2O3 ( , , X Li Na K  ) as the reference systems at high temperature. Due to the lack of satisfactory potentials that can produce reliable room temperature samples for all of the alkali borates, the procedure discussed in our previous work 27 to produce samples at room temperature needed for the optimization was slightly modified as described below.…”

“…In our previous work 27 , we used an optimization scheme similar to the one developed for silica 28 and extended the interaction parameter set to include alkali modifiers lithium, sodium and potassium, alkaline earth modifier calcium, and aluminum that can behave as a modifier or a former depending on the composition 29,30 . In this work, we adapt a similar optimization approach to include the network former boron into our parameter set to allow MD simulations of glasses with mixed network formers.…”