Orientation of H center and adsorptivity of atomic H on LiH(001) surface: ab initio study

Abstract

An embedded cluster method was used to examine the relative stabilities of H center orientations in the bulk of LiH as well as the effects of the H center on the adsorptivity of atomic H using the second order Moller–Plesset perturbation level of ab initio theory. The clusters were embedded in a simulated Coulomb field that closely approximates the Madelung potential of the host. The 〈111〉 orientation was found to be more stable than the 〈110〉 orientation by ca. 0.871eV. An appreciable spin density redistribution on the H2− molecular ion of the 〈111〉 and 〈110〉 orientations is observed. The H center improves the adsorptivity of atomic H on some sites by ca. 15.5eV but disproves the adsorptivity on others by ca. 5.76eV and enhances the electrical properties of the crystal. The diffusivity of atomic H over the surface is severely restricted by H center imperfection and the electrostatic curves explain the exclusive effects of H center on the adsorptivity and mobility of atomic H. As the H center is introduced, the top of the valence band and the bottom of the conduction band shift to lower energies and the valence–conduction band gap is reduced. This change in the electronic structure makes spin pairing between the singly occupied atomic orbital of H and the singly occupied molecular orbital of substrate more facile in the course of adsorbate–substrate interactions.