Thermal properties of the self-interstitial in aluminum: An ab initio molecular-dynamics study

An order-N ab initio molecular-dynamics method, based on orbital-free density functional theory, is applied to the study of the interstitial in aluminum. The results confirm the 〈100〉 dumbbell (in which two atoms occupy a single lattice site, forming an atom pair in the 〈100〉 direction) as the lowest-energy structure, with a formation energy {~}0.2 eV lower than the classical octahedral interstitial. Formation of the interstitial is associated with a reorganization of the atomic and electronic structure, which extends over several unit cells. The dumbbell interstitial is shown to have a low-energy ({~}0.084 eV) migration pathway and to be responsible for the appearance of low-frequency resonance modes in the vibrational density of states.