Identifying deformation mechanisms in molecular dynamics simulations of laser shocked matter

Abstract

In this paper we demonstrate a new post-processing technique that allows straightforward identification of deformation mechanisms in molecular dy- namics simulations. We utilise reciprocal space methods by calculating a per-atom structure factor (PASF) to visualise changes in volume, orienta- tion and structure, thus allowing unambiguous discrimination between key deformation/relaxation mechanisms such as uniaxial strain, twinning and structural phase transformations. The full 3-D PASF is reduced to a 2-D representation by taking only those points which lie on the surface of an el- lipsoid passing through the nearest reciprocal lattice points. Projecting this 2-D representation onto the set of spherical harmonics allows for a numerical characterisation of the system state that easily captures various plastic de- formation mechanisms that have been historically difficult to identify. The technique is used to successfully classify high temperature twinning rotations in shock compressed tantalum and to identify the α to ω phase transition in group-IV hcp metals.