Reorientation of self-trapped hole and adsorptivity of atomic hydrogen on LiH (001) surface: ab initio study

An ab initio embedded molecular cluster method was used to examine the bulk and surface orientations of the self-trapped hole (STH), activation barrie rs for diffusion of STH along the (110) axis and the effect of STH on the a dsorptivity and mobility of atomic II over the surface using the Hartree-Fo ck approximation and Moller-Plesset second order perturbation correction. T he "on-center" configuration of the doubler ground state is energetically m ore favored than the "off-center" configuration and the correlated activati on barriers are 0.36 and 0.25 eV for bulk and surface diffusion. The positi ve hole is localized along the (110) axis mainly at the anion vacancy sites and partially at the center of mass of the molecular ion. The STH enhances the adsorptivity of atomic hydrogen by similar to 3.5 eV at the correlated level, changes the nature of adsorption from physisorption to chemisorptio n and restricts the mobility of atomic II over the surface. As the STH is i ntroduced to the crystal surface, the HOMO and LUMO levels shift to lower e nergies and the valence-conduction band gap broadens. This change in the el ectronic structure makes spin pairing between adsorbate singly occupied ato mic orbital and substrate singly occupied molecular orbital more facile in the course of adsorbate-substrate interactions. (C) 2000 Elsevier Science L td. All rights reserved.