Accelerated Molecular Dynamics through stochastic iterations to strengthen yield of path hopping over upper states (SISYPHUS)

TL;DR

SISYPHUS is a novel atomistic simulation method that combines stochastic and molecular dynamics techniques to extend accessible time-scales, accurately model transition events, and avoid harmonic transition state theory limitations.

Contribution

The paper introduces SISYPHUS, a new method that separates phase space into basins and transition regions, improving time-scale extension and transition event sampling in atomistic simulations.

Findings

Successfully applied to vacancy diffusion in BCC Ta

Demonstrated effectiveness in adatom island ripening in FCC Al

Provides accurate real-time scale without enumerating all transitions

Abstract

We present a new method, called SISYPHUS (Stochastic Iterations to Strengthen Yield of Path Hopping over Upper States), for extending accessible time-scales in atomistic simulations. The method proceeds by separating phase space into basins, and transition regions between the basins based on a general collective variable (CV) criterion. The transition regions are treated via traditional molecular dynamics (MD) while Monte Carlo (MC) methods are used to (i) estimate the expected time spent in each basin and (ii) thermalize the system between two MD episodes. In particular, an efficient adiabatic switching based scheme is used to estimate the time spent inside the basins. The method offers various advantages over existing approaches in terms of (i) providing an accurate real time scale, (ii) avoiding reliance on harmonic transition state theory and (iii) avoiding the need to enumerate all possible transition events. Applications of SISYPHUS to low temperature vacancy diffusion in BCC Ta and adatom island ripening in FCC Al are presented. A new CV appropriate for such condensed phases, especially for transitions involving collective motions of several atoms, is also introduced.