Hybrid QM/MM embedding approach for the treatment of localized surface states in ionic materials

We present a hybrid quantum mechanical/molecular mechanical technique recently developed and implemented in the computational chemistry software environment, ChemShell, aimed at the study of reactions at the surfaces of ionic solids including reconstructed polar surfaces and interfaces. The method follows approaches commonly used for the treatment of point defects in the bulk of halide and oxide materials but also incorporates surface-specific relaxation and electrostatic effects, which allows one to study adsorption of charged and strongly dipolar species as well as inherent structural and electronic surface defects. Applications of this embedding approach are illustrated with the investigation into electron trapping at the oxygen terminated polar surfaces of ZnO and related surface F centers. Processes discussed are of particular interest for heterogeneous catalysis as the species characterized prove to be active catalytic centers in methanol synthesis over ZnO. (C) 2004 Wiley Periodicals, Inc.