Hyperdynamics Approaches to Energetically and Entropically Rare Events

Steve Stuart
Clemson University
Department of Chemistry

The hyperdynamics method provides a way of performing dynamics on a biased potential while still retaining valid kinetics (in at least a statistical sense). The bias potential can be constructed so that rare events are sampled more frequently, and knowledge of the bias potential can be used to recover dynamic information on the unbiased potential. However, there are still open questions about how to best construct the bias potential for a given application, and what constraints a bias potential must satisfy in order to produce accurate hyperdynamics trajectories. Two applications of hyperdynamics will be discussed that help answer these questions. One is an application to rare covalent bond-breaking reactions in the pyrolysis of hydrocarbons. Careful construction of bias potentials can be used to achieve speedups of approximately 50x, allowing simulations at more realistic temperatures than on unbiased potentials. Lessons can also be learned about the types of bias potentials that are most successful for this class of reactive systems. In the second application, hyperdynamics is applied to rare-event systems with purely entropic barriers. The construction of bias potentials for such a system appears problematic, as all biases will exceed the transition state energy. Nonetheless, nontrivial speedups of nearly tenfold can be achieved in artificial systems, and several of the resulting conclusions about bias potential construction can be applied to more realistic systems with entropic barriers.

Back to Workshop II: Multiscale Modeling in Condensed Matter and Materials Sciences, including Mini-Workshop: Time Acceleration Methods in Atomistic Simulations