Migration Energy of an Interstitial He Atom in LiH

Abstract

The method of lattice statics is used to study the distortion of the LiH crystal with an interstitial He atom in the body-centered or face-centered position. In these calculations, one needs to know the defect-host-ion interaction potentials and the dynamical matrix of the undistorted host crystal. The Heitler-London method is used to estimate the defect-host-ion interaction potentials. The dynamical matrix of the perfect crystal is calculated on the basis of the deformation dipole model. The formation energies are computed for the two defect positions and their difference, 0.650 eV, gives the migration energy of an interstitial He atom in LiH. The calculated migration energy is discussed in light of the high-temperature experimental result for the activation energy of diffusion of He gas in LiH crystal (1.22 eV).