Theoretical Study of Cluster-Lattice Interaction and Defects in Ionic-Crystals

Abstract

An anempt has bttn made to examine the bulk and surface properties of exciton bands near F+, F and reenters (Cl, andY bands}, diffusion of electron centers(.F and F-) and adsorptivity of atomic Hover the defect free and d fea containing surfaces of Lif and NaH isoelec:tronic: c:rystals using an ab initio embedded c:luster model 81 the second order Mo'llcr-Picssct perturbation level. The UF and NaH c:lusters were embedded in simulated Coulomb fields that c:losely approximate the Madelung potentials of the host crystals. The isocledronic LiF and NaH clusters in crystals were found 10 exhibit distinct differences in the title properties. The defect free and F+ band gaps and exciton bands ofLiF were significantly greater than those ofNaH.The LiF aystal was more sensitive to the relaxation effects than NaH. The activation energy barriers to the electron center diffusion hops in UF were: always greater than those in NaH. The H atom adsorbs more: strongly on the defcct free.and rsurfaces ofNaH relative to UF.The reported changes in band structure due to surface imperfection explain the dramatic: increase of atomic H adsorption over F and rsurfac:cs ofUF and NaHas well as the preferred stability of atomic Hover the defec:t free and t+ dcfed containing surfaces ofNaH in the course of adsorbate substrate internctions. The reported differences in properties arc possibly anributed to the differcnc:es in the Janic:e interionic interactions and lhe extended charge distribution of the hydride anion.