Variable timestep algorithm for molecular dynamics simulation of non-equilibrium processes

Abstract

A simple, yet robust variable timestep algorithm is developed for use in molecular dynamics simulations of energetic processes. Single-particle Kepler orbits are studied to study the relationship between trajectory properties and the critical timestep for constant integration error. Over a wide variety of conditions the magnitude of the maximum force is found to correlate linearly with the inverse critical timestep. Other quantities used in the literature such as the time derivative of the force and the product of the velocity and force also show reasonable correlations, but not to the same extent. Application of the corresponding metric ||Fmax||Δt in molecular dynamics simulation of radiation damage in graphite shows that the scheme is both straightforward to implement and effective. In tests on a 1keV cascade the timestep varies by over two orders of magnitude with minimal loss of energy conservation.