Bulk dislocation-U defect interaction, surface excitons and adsorptivity of atomic H on dislocated surfaces of LiH crystal: ab initio calculations

An ab initio embedded cluster method was used to examine the bulk dislocati on-U defect interaction, surface excitons and the adsorptivity of atomic H on dislocated surfaces of LiH using the Hartree-Fock approximation and the second-order Moller-Plesset perturbation correction. In the LIH crystal bul k, the results confirm: (1) U-1 and U-2 centres make dislocations more faci le, (2) dislocation processes do not reduce the ionic conductivity of highl y populated edge centred hydride interstitials and (3) the dislocation-U de fect interaction increases monotonically in the series face --> volume --> edge centred interstitial structures. On LiH crystal surfaces the results c onfirm: (1) the exclusive dependence of band gaps and exciton bands on disl ocation, (2) the strongest adsorption of atomic H on a surface is associate d with X-dislocations, (3) dislocations are unable to change the nature of physical adsorption to chemical adsorption and (4) the mobility of atomic H over the Z-dislocated surface is more facile than that over the X-dislocat ed surface. As X-surface dislocation proceeds, the HOMO and LUMO levels of the substrate shift to higher energies and the band gap becomes narrower. T his change in the electronic structure suggests that charge transfer from t he X-dislocated surface is more facile in the course of adsorbate-substrate interaction.