Large-scale DFT calculations of multi-component glass systems (SiO2)0.70(Al2O3)0.13(XO)0.17 (X = Mg, Ca, Sr, Ba) : Accuracy of classical force fields

Although molecular dynamics (MD) simulation is a powerful tool for investigating the atomic-scale structures of complex materials, several challenges limit their reliable and accurate application to multi-component glass systems. The available force fields (FFs) that can treat many elements in a multi-component glass are limited, and even if such a FF exists, its accuracy is suspicious due to the large variety and complexity of chemical environments in these materials. First-principles calculations based on the density functional theory (DFT) are reliable, but prohibitively expensive with conventional methods.
In this study, we use large-scale DFT techniques and demonstrate that it is possible to perform efficient and accurate DFT calculations of multi-component glass systems, such as (SiO$_2$)$_{0.70}$(Al$_2$O$_3$)$_{0.13}$($X$O)$_{0.17}$ ($X$ = Mg, Ca, Sr, Ba), containing about 1,000--5,000 atoms.
From the results of large-scale DFT calculations, we evaluate the accuracy of some classical FFs,
and show that the accuracy for non-bridging oxygen atoms is very low especially when the Si--O distance is short. Large differences in the distribution of Si--O--Si angles observed in the FF-MD and DFT-MD simulations
and the unique electronic structure in the case of $X$=Mg are also discussed.