Prediction of dislocation nucleation during nanoindentation by the orbital-free density functional theory local quasi-continuum method

We introduce the orbital-free density functional theory local quasi-continuum (OFDFT-LQC) method: a first-principles-based multiscale material model that embeds OFDFT unit cells at the subgrid level of a finite element computation. Although this method cannot address intermediate length scales such as grain boundary evolution or microtexture, it is well suited to study material phenomena such as continuum level prediction of dislocation nucleation and the effects of varying alloy composition. The model is illustrated with the simulation of dislocation nucleation during indentation into the (111) and (110) surfaces of aluminum and compared against results obtained using an embedded atom method interatomic potential. None of the traditional dislocation nucleation criteria ( Hertzian principal shear stress, actual principal shear stress, von Mises strain, or resolved shear stress) correlates with a previously proposed local elastic stability criterion, Lambda. Discrepancies in dislocation nucleation predictions between OFDFT-LQC and other simulations highlight the need for accurate, atomistic constitutive models and the use of realistically sized indenters in the simulations.