Interstitial diffusion of a helium atom in bulk Li4SiO4 crystal from first-principles calculations

The interstitial stability and diffusion properties of helium in Li4SiO4 crystals are studied by using density functional theory (DFT) simulation. All types of interstitial sites are established. Possible helium locally stable (LS) positions in interstitial sites are examined, and the formation energies are calculated. The LS site of helium interstitial in Li4SiO4 crystals is determined, the diffusion paths and barriers of the helium between adjacent LS sites are calculated by the CI-NEB method. The results show that there are 11 different LS sites in the Li4SiO4 crystal, and the formation energies are in the range of 0.770–1.034 eV. Using CI-NEB calculations, we find that the diffusion of helium is anisotropic along different directions. The most favorable diffusion path appears at the center of the crystal and diffusion along the direction, and the diffusion barrier is 0.16 eV. © 2019