Z(1) center orientation and adsorptivity of atomic hydrogen at LiH (001) surface: DFT calculations

An attempt has been made to examine the relative stabilities of Z(1) center orientations at the surface of LiH crystal as well as the effects of Z(1), center on the adsorptivity of atomic hydrogen using an embedded cluster mo del and density functional theory calculations. The embedded clusters were terminated by point ions and partial ionic charges that make the Coulomb po tential at the central surface sites equal to the Madelung potential of the host surface. The linear orientation of the present Z(1) center was more s table than the nonlinear orientation by ca. 0.16eV and the center is sugges ted to be an F center strongly perturbed by a neighboring positive ion vaca ncy V- and almost independent on the divalent positive ion Be2+. The atomic hydrogen adsorbs more strongly at the anionic sites rather than the cation ic sites of the defect free surface. The Z(1) center enhances the adsorptiv ity of the atomic hydrogen at the Be2+ and F sites of the defect containing surface by ca. 2.43 and 2.19 eV, respectively and changes the nature of ad sorption on these sites from physical adsorption to chemical adsorption. Th e contributions to the adsorbate-substrate interactions were explainable in terms of surface electrostatic potentials and the spin pairing mechanism p lays the dominant role in the course of the adsorbate-substrate interaction s. The center reduces the valence- conduction band gap by ca. 2.76 eV and c hanges the nature of the surface from insulating surface to semiconducting surface. (C) 2001 Elsevier Science B.V. All rights reserved.