Be2+V- dipole and adsorptivity of atomic H on LiH(001) surface: ab initio study

An attempt has been made to examine the properties of the title divalent ca tion impurity cation vacancy dipole as well as the adsorptivity and diffusi on of atomic hydrogen over the LiH (001) surface using ab initio methods of molecular electronic structure calculations. The LiH crystal surface was s imulated and quantum clusters of variable size were surrounded by point cha rges to examine the I-V dipole orientation, cation vacancy migration and ov erlap effects. The effects of introducing an I-V dipole on the nature of ad sorbate-substrate interactions and diffusion of an H atom over the surface were also examined. The results confirm that the (100) orientation of the I -V dipole is energetically more favorable than the (110) orientation and th at the cation vacancy migrates without activation energy barriers. The I-V dipole enhances the adsorptivity of atomic hydrogen by ca. 4.96 eV, changes the nature of adsorption from physisorption to chemisorption and introduce s an activation energy barrier to H diffusion over the surface. As the I-V dipole is introduced, the HOMO and LUMO levels of the substrate shift to hi gher energies, the band gap becomes narrower and the atomic charges on the adsorbed H increases. This change in the electronic structure makes the ads orptivity process, through the charge transfer from the H 1s singly occupie d AO to the conduction band and from the valence band to the H 1s singly oc cupied AO more facile.