Adaptive Strain-Boost Hyperdynamics Simulations of Stress-Driven Atomic Processes

The deformation and failure phenomena of materials are the results of stress-driven, thermally activated processes at the atomic scale. Molecular-dynamics (MD) simulations can only span a very limited time range which hinders one from gaining full view of the deformation physics. Inspired by the Eshelby transformation formalism, we present here a transformation “strain-boost” method for accelerating atomistic simulations, which is often more efficient and robust than the bond-boost hyperdynamics method [R. A. Miron and K. A. Fichthorn, J. Chem. Phys. 119, 6210 (2003)] for exploring collective stress-driven processes such as dislocation nucleation, that have characteristic activation volumes larger than one atomic volume. By introducing an adaptive algorithm that safely maximizes the boost factor, we directly access the finite-temperature dynamical process of dislocation nucleation in compressed Cu nanopillar over time scale comparable to laboratory experiments. Our method provides stress- and temperature-dependent activation enthalpy, activation entropy and activation volume for surface-dislocation nucleation with no human guidance about crystallography or deformation physics. Remarkably, the accelerated MD results indicate that harmonic transition-state theory and the empirical Meyer-Neldel compensation rule give reasonable approximations of the dislocation nucleation rate.