SPOCK: Exact Parallel Kinetic Monte-Carlo on 1.5 Million Tasks

We have created a scalable implementation of the kinetic Monte-Carlo method, SPOCK (Scalable Parallel Optimistic Crystal Kinetics). Unlike most reported parallel implementations relying on approximation to achieve parallelism, our parallelization is exact and accomplished using the Time Warp paradigm. We demonstrate that our implementation exhibits near perfect scaling for two different and important classes of systems. It runs efficiently on Vulcan, a 24 thousand node BlueGene/Q machine, using all ~400 thousand cores and ~1.6 million MPI tasks. Further, we have run production simulations using the full Vulcan machine and requiring nearly all available system memory. In this paper we demonstrate these results, and discuss some important implementation details. The kinetic Monte-Carlo method is ubiquitous within the natural sciences, and important classes of problems have so far been limited to sequential simulation. For many scientific simulations, an exact parallel implementation of the kinetic Monte-Carlo method has the potential of being game changing.