Parallel athermal quasistatic deformation stepping of molecular systems

Abstract

The athermal quasistatic deformation method provides an elegant solution to overcome the limitation of short time spans in molecular simulations. It provides overdamped conditions, allowing for the extraction of purely structural responses in the absence of thermal vibration. However, it requires computationally expensive sequences of affine deformation followed by minimization of the potential energy to incrementally find the path in the potential energy landscape that corresponds to the correct solution trajectory. Therefore, we propose an athermal parallel stepping scheme that significantly improves the computational time necessary to find the correct solution trajectory using a multi-thread approach. Our approach proposes stepping at two levels. Level I stepping provides a sequence of initial guesses at large increments by affine deformation of the system and land-marking anchor points on the potential energy landscape. Level II stepping performs a set of individual finely resolved athermal quasistatic deformation steps between the inherent structures of the initial level I guesses executed in parallel. The evaluated candidate trajectory is then verified by consecutively comparing the configuration of every last level II result with the corresponding inherent structure of the level I guesses at the same strain states. If the two configurations are not equivalent, the solution must be rejected and recalculated from this point. Rigorous numerical testing with $4,8,16$ and $32$ parallel threads and different values of hyper-parameters demonstrates that our method achieves computational average speed-ups of factors ranging from $2.02$ to $6.33$, while maintaining simulation accuracy, offering a powerful new tool for athermal molecular simulations.