AM1 and MNDO semiempirical electronic calculations have been carried out for ZnO surface ((ZnO)n, n = 11, 16, 22, 24, 33, 42, and 44) cluster models. The theoretical results can be summarized as follows: (i) the energy gap HOMO–LUMO is shown to be dependent on the cluster size and geometry optimization; however, better agreement of this gap with experimental data is obtained with cluster of limited size (n = 16, 22, and 24). (ii) The Mulliken charge of the cluster zinc ion is invariant with the optimization procedure, showing an average value of 0.52 a.u. (MNDO) and 0.62 a.u. (AM1). © 1993 John Wiley & Sons, Inc.