Research Topic

[Hyper-QC] Topic: Hyper-QC

Team: Woo Kyun Kim (U. Cincinnati), Ellad Tadmor

Collaboration: Art Voter (LANL), Danny Perez (LANL), Mitch Luskin (U. Minnesota)

Funding: Pending

Figure: A hyper-QC simulation of nanoindentation into a nickel single film. The ability of the method to span multiple length and time scales makes it possible to simulate a sufficiently large system to preclude boundary effects at near to realistic loading rates.

Description: The finite temperature quasicontinuum method (aka "hot-QC") is a spatial multiscale method that extends the length scales accessible to fully-atomistic molecular dynamics (MD) simulations by several orders of magnitude. However, the times accessible to these simulations remain limited to a sub-microsecond time scale due to the small time step required for stability of the numerical integration. To address this limitation, we develop a novel hot-QC method that can treat much longer time scales by coupling hot-QC with hyperdynamics – a method for accelerating time in MD simulations. We refer to the new approach as "hyper-QC". As in the original hyperdynamics method, hyper-QC is targeted at dynamical systems that exhibit a separation of time scales between short atomic vibration periods and long waiting times in metastable states. Acceleration is achieved by modifying the hot-QC potential energy to reduce the energy barriers between metastable states in a manner that ensures that the characteristic dynamics of the system are preserved. A hyper-QC simulation of nanoindentation has led to an interesting observation regarding to the entropic nature of dislocations (see Kim and Tadmor (2014) below). The hyper-QC methodology is currently being extended and applied to applications of interest.