Z1, center orientations and adsorption of atomic halogens at the (001) surfaces of Alkaili Chloride Crystals: DFT Calculations.

Abstract

An attempt has been made to examine the relative stabilities of Z, center orientations at the surfaces of Be2+, Mg2+ and Ca2+ doped LiCl, NaCl and KC1 ionic crystals as well as the effects of Z, center on the adsorption of atomic halogens (F, Cl, Br, I and At) using an embedded cluster model and density functional theory calculations. The embedded clusters were terminated by partial ionic charges that make the Coulomb potentials at the central surface sites equal to the Madelung potentials of the host.surfaces. While the linear orientations of the Be2+ doped surfaces were more stable than the non linear orientations, the non linear orientations of Mg2+ and Ca2+ doped surfaces were more stable than the linear orientations. The Z, center is suggested to be an F center strongly perturbed by a neighboring monovalent cation vacancy and almost independent on the position of the divalent cation impurity. The relative stabilities were neither dependent on the type of the divalent cation impurity nor the type of the monovalent hdst cation. The Z, center changes the nature of atomic halogen adsorption from physical adsorption to; chemical adsorption and the adsorption energies are directly proportional to the electronegativity of the halogen and the effec¬ tive nuclear charge of the host cation. The spin pairing mechanism plays the dominant role in the course of adsorbate-substrate interactions, and the surfaces can be made semiconducting by Zt center imperfec¬ tion.