DENSITY-FUNCTIONAL CLUSTER DESCRIPTION OF IONIC MATERIALS - IMPROVED BOUNDARY-CONDITIONS FOR MGO CLUSTERS WITH THE HELP OF CATION MODEL POTENTIALS

Ionic materials can be conveniently described by quantum mechanical cl uster models. In these models the electrostatic field of the crystal s urrounding is often taken into account by embedding the cluster in an array of point charges (PCs). However, anions at the cluster boundary can be strongly polarized by neighboring positive PCs. These artifacts can be significantly reduced if a model potential description is empl oyed for the nearest-neighbor cations of the surrounding. We have impl emented a scheme of total ion model potentials (TIMP) in the density f unctional code LCGTO-DF. in the present work we compare a number of el ectronic properties of MgO(001) models, like core-level splittings, el ectron affinity, and electrostatic potential, computed with the help o f TIMP embedding to results obtained for the same clusters surrounded by PCs only. The cluster models range from MgO58- to Mg25O25. Adsorpti on of a CO molecule on TIMP embedded cluster models of a regular surfa ce site and the three-coordinated corner Mg2+ site is also considered. (C) 1997 John Wiley & Sons, Inc.