Molecular Dynamics Simulations of Graphite at High Temperatures

Graphite, a key structural and moderator material in the proposed Generation IV roadmap, is expected to experience irradiation at temperatures up to 1800 K. In this study, a molecular dynamics (MD) code is developed for the purpose of performing atomistic simulations of high-temperature graphite. The MD computations are benchmarked against thermal expansion and mean-squared displacement data, and modifications to the potential energy function are devised as needed to fit experimental measurements. Graphite-specific alterations include a plane-by-plane center-of-mass velocity correction, anisotropy in the potential energy cutoff function, and temperature-dependent parameterization of the interatomic potential. The refined MD model is then employed to investigate the threshold displacement energy at temperatures of 300 and 1800 K. It was found that the threshold displacement energy depends strongly on the knock-on direction, yet the angle-averaged threshold energy exhibits relatively little variation with temperature.