*2.2. MD Simulation Setup*

An MD simulation programme, LAMMPS (7Aug19 version) [46], is employed herein for all simulations. Images of atomic configurations were produced with the visualisation tool OVITO (3.5.0 version, Darmstadt, Germany) [46]. The Wigner–Seitz (W–S) cell method determined the type and position of the interstitial atoms or vacancies [47,48]. The time step was set as 0.001 ps for all MD simulations. The temperature was controlled via a Nose/Hoover temperature thermostat, and the periodic boundary condition was used. For static relaxation, the energy minimisation was performed, and the minimisation algorithm was set as the conjugate gradient method (cg). The specific simulation processes for different behaviours differ, and the details of the different simulations are described as follows.
