CORRELATION BETWEEN THE MADELUNG FIELD AND THE REACTIVITY OF THE MGO LOW-COORDINATED SURFACE SITES

We study correlations between Madelung constants, charges of surface ions, and chemical activity of low-coordinated sites of the MgO crystal surface with respect to dissociative adsorption of hydrogen. The ab initio Embedded Cluster model [Puchin et al., Phys. Rev. B 47, 6226 (1993)] employed in this study allowed us to reproduce correctly both short range and long range (Madelung) parts of the interaction between ions in a quantum cluster and the rest of the crystal. Our results show that sites having the same coordination numbers may have different properties, depending on values of Madelung constants. Lower Madelung constants correspond to lower ionicity, higher energy of H2 adsorption, stronger O-H and Mg-H bonds, and larger spatial separation of two adsorbed hydrogen atoms. © 1995 American Institute of Physics.