First-principles molecular dynamics compression of small metallic nanoparticles

Whether the strength of materials keeps increasing, saturates or decreases when characteristic dimensions are reduced down to the nanometer scale remains an open question. To bring new insights, first principles molecular dynamics calculations are performed to model the compression of 1-2 nm aluminum nanoparticles with different shapes. We find that the plastic deformation occurs at high strains and stresses by a mechanism combining diffusive and displacive atomic displacements. This deformation mode is characterized by a slow dynamic and the partial or even complete recovery of crystalline order. The strength depends on the nanoparticles shape, and is in all cases significantly higher than the theoretical bulk strength. It is however substantially lower than values extrapolated using reported classical molecular dynamics investigations. Our results suggest that the strength saturates at low scales.