MANY-BODY EXPANSION AND ION DIFFUSION IN LIH CRYSTAL

A finite LiH lattice whose Madelung potential in the central region cl osely approximates the Madelung potential in the host crystal is const ructed. Hartree-Fock calculations were then carried out on lithium hyd ride clusters both within the crystal and as isolated species. The man y body expansion terms and the probability of ionic motions which resu lt in diffusion are examined and relaxation around diffused ions is ta ken into account. Calculations confirm that the many body expansion te rms in the crystal environment are both convergent and smaller than fo r the isolated clusters. The two-ion rotation mechanism is the most pr obable. The barrier height for cation diffusion is less than for anion diffusion suggesting easier transfer of cations rather than anions wi thin the LiH crystal. The results are correlated with those reported p reviously on LiF crystal. (C) 1997 Elsevier Science Ltd.