We have used the Oniom method with three layers in order to study the interaction of CO, H 2, H 2O, NH 3 and CO 2 molecules with the ZnO (101̄0) surfaces using a (ZnO) 348 cluster model. The layers are divided into the high layer at the CCSD level, the medium layer at the RHF level and the low level layer using the UFF force field method. The orbital and binding energies of the adsorbed molecules, Mulliken and ChelpG charges as well as geometrical parameters were analyzed and compared with the available experimental and theoretical data. © 2004 Elsevier B.V. All rights reserved.