Molecular dynamics simulations of elastic response and tensile failure of alumina

We present the results of molecular dynamics simulations of alpha-alumina performed using the ES+ potential. We concentrate here on the applicability of these potentials to the study of surface structure and thin film elastic response. The aluminum-terminated (0001) surface of alpha-alumina is found to undergo dramatic relaxation away from bulk values, driven by the electrostatics of atoms near the surface. We find that the local valence is reduced by 25% for surface and near-surface atoms in this orientation. We demonstrate that the strain variation of the elastic constants in a 25 Angstrom thick film of alpha-alumina can differ substantially from the expected behavior in a bulk crystal. The thin film was found to yield at a stress of approximately 45 GPa, in agreement with a calculation of the theoretical limit of yield stress.