Origin of the elastic anisotropy of silica particles: Insights from first-principles calculations and nanoindentation molecular dynamic simulations

To better elucidate and comprehend the origin of the elastic anisotropy observed in silica sand, this study in-vestigates the nanoscale mechanical properties of a-quartz (the main component of silica sand) using the first-principles calculations (density functional theory, DFT) and nanoindentation molecular dynamics (MD) simu-lations. The cell parameters and elastic constants (Cij) of a-quartz are obtained by DFT with PBESOL functional. The electron density difference of the most commonly exposed crystal surfaces {100}, {001}, and {101}, ex-hibits significant distinction, which is considered as the underlying cause of a-quartz's elastic anisotropy. This study reveals a significant difference in Young's modulus E, Poisson's ratio v, and hardness H along different directions, which are also visualized in three dimensional graphics. Notably, E{10 0} = 81.576 GPa < E{0 0 1} = 101.198 GPa < E{1 0 1}= 113.323 GPa, and H{0 0 1} = 9.068 GPa < H{1 0 0}= 11.258 GPa < H{1 0 1} = 19.870 GPa. The change in E calculated by MD simulations is consistent with DFT calculations. Additionally, this study observed distinct initiation of yielding during nanoindentation for different crystal surfaces, with the corre-sponding indentation yielding depth following the trend D{1 0 0} > D{0 0 1} > D{1 0 1}. Furthermore, both DFT and MD simulation results indicate that the negative v effect on E is negligible in a-quartz.