Di-interstitial diffusivity and migration path calculations based on tight-binding Hamiltonian molecular dynamics

Molecular dynamics calculations were performed for di-interstitial-silicon based on the tight-binding model for silicon. Calculation results indicate that the di-interstitial can diffuse into crystalline silicon as fast as the mono-interstitial silicon. Three kinds of the stable configurations were found: T, Z, and W-configuration. The T-configuration is the lowest while the W is the higher energy level configuration. A critical-path method (a saddle-point search algorithm) revealed the di-interstitial migration pathway. The T to W transition needs about 0.96 eV of the barrier energy, and the W to W transition can occur for less than 0.1 eV barrier energy. Therefore, di-interstitials can show a long-range hop via the W-W transition which should be thermally initiated by the T-W transition (reorientation).