AB-INITIO STUDY OF A CO MONOLAYER ADSORBED ON THE (10(1)OVER-BAR-0) SURFACE OF ZNO

Periodic Hartree-Fock total energy calculations on two-dimensionally p eriodic slabs have been used to predict the equilibrium geometry of a monolayer of carbon monoxide molecules adsorbed on the nonpolar (<10(1 )over bar 0>) surface of ZnO. Two physisorbed (or weakly chemisorbed) minimum energy configurations are found. In one the CO molecules adsor b with their oxygen atoms coordinated to surface Zn atoms, while in th e other the carbon atoms are coordinated to surface Zn atoms. The two calculated minima are very close in energy. In the second geometry, th e C-Zn ''bond'' and the C-O bond make angles of 32.5 degrees and 39.5 degrees with the surface normal, and the intramolecular bond shortens slightly from its free value in reasonable agreement with experimental results. No binding of CO to the surface oxygen atoms is predicted. S urface-related changes in the vibrational frequencies for the adsorbed molecules agree reasonably well with infrared spectroscopic data, and the ''carbon-down'' binding energy of the molecule with the surface i s in good agreement with thermal desorption data (though electron corr elation effects have to be included in the calculation to obtain accep table results for low surface coverage). (C) 1996 American Institute o f Physics.