Quantum Mechanical Description of Displacement Damage Formation

Atomic-scale processes during displacement damage formation have been previously studied using molecular dynamics (MD) calculations and empirical potentials. Low-energy displacements (< 1 keV) are characterized by a high cross-section for producing secondary knock-on atoms and damage clusters, and determine the threshold displacement energy (an important parameter in NIEL calculations). Here we report first-principles, parameter-free quantum mechanical calculations of the dynamics of low-energy displacement damage events. We find that isolated defects formed by direct displacements result from damage events of <= 100 eV. For higher energy events, the initial defect profile, which subsequently undergoes thermal annealing to give rise to a final stable defect profile, is the result of the relaxation and recrystallization of an appreciable volume of significantly disordered and locally heated crystal surrounding the primary knock-on atom displacement trajectory.