Crystalline and amorphous models of highly damaged Fe

The structure of irradiated material near a primary knock on atom shortly after impact is largely unknown. Molecular dynamics simulations with classical force fields provide the foundation for our current understanding of the resulting cascade. Atomic level structural characterization is often in terms defects within the context of a perfect bulk, however, the choice of the best representation is complicated because the density of defects is high, the material is inhomogeneous and it is not in equilibrium. Here we explore the adaptation of tools typically employed to characterize homogeneous equilibrium liquids to the highly defected region of the cascade. The cascade structure shows some resemblance to that of the liquid or glass phase. The local temperature temporarily exceeds the melting temperature and the free energies of the liquid and defected crystal are comparable. Analysis of cascade structure will be important to the interpretation of first principles calculations of the electronic and magnetic states in cascade structures.