Hyperdynamics simulation of surface diffusion and clustering

This work is by Steve Plimpton (Sandia) and Danny Perez and Art Voter (LANL) using the accelerated MD method known as local hyperdynamics to simulate the surface diffusion of adatoms on a Pt(100) surface. A large 2.4 million atom simulation (half of them mobile) with 4% adatoms (~12,000) randomly placed on the surface was run for 32 million timesteps using a time boost factor of 1000x, so that the surface evolved at 400K for 160 us. The simulation was performed on 64 nodes of the Theta supercomputer (Intel KNL nodes) at Argonne’s ALCF facility. Adatoms grew into clusters as large as 15 atoms over this timescale.

The first image shows common events that adatoms undergo when they are part of isolated monomers, dimers, or trimers. Almost all events in this system involve exchanges between adatoms and substrate atoms. The second and third images are the initial and final snapshots from a movie of the full system. Orange atoms are in the substrate. Black adatoms are monomers. White adatoms are in clusters. The movie was made from simulation snapshots rendered by Mitch Wood (Sandia) using the Ovito visualization package.