A CLUSTER APPROACH FOR MODELING OF SURFACE CHARACTERISTICS OF STANNICOXIDE

An ab initio cluster approach (LDA-SCF) is used to study the electroni c structure of the SnO2 (110)-1 x 1 surface without any relaxation and reconstruction. Modelling is made for the ideal nonpolar surface and also for surfaces containing different kinds of oxygen vacancies, fore ign impurities and adsorbates. Computations are based on the linear co mbination of atomic orbitals (LCAO), which allows the population analy sis through projection of the molecular orbitals onto the atomic basis set. This is used to trace the atomic character of the cluster levels . A cluster with 103 atoms Sn32O71 is used to model the ideal SnO2 (11 0) surface, the most stable and thus the dominant crystallite face of the polycrystalline SnO2, and the next few bulk layers. The results he re refer to both the ideal nonpolar (110) surface and some oxygen-defi cient polar (110) surfaces. Chromium and NO are taken as examples of i mpurity atoms and adsorbate molecules, respectively. Based on the resu lts we are able to suggest an explanation for the observed strong decr ease of conductivity of SnO2 polycrystalline films and the enhanced ad sorption and dissociation of NO on the SnO2 surface due to adding of c hromium impurities.