A cluster approach for modelling of surface characteristics of stannic oxide

An ab initio cluster approach (LDA-SCF) is used to study the electronic structure of the SnO₂ (110)-1 × 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, foreign impurities and adsorbates. Computations are based on the linear combination of atomic orbitals (LCAO), which allows the population analysis 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 (110) surface, the most stable and thus the dominant crystallite face of the polycrystalline SnO₂, and the next few bulk layers. The results here refer to both the ideal nonpolar (110) surface and some oxygen-deficient polar (110) surfaces. Chromium and NO are taken as examples of impurity atoms and adsorbate molecules, respectively. Based on the results we are able to suggest an explanation for the observed strong decrease of conductivity of SnO₂ polycrystalline films and the enhanced adsorption and dissociation of NO on the SnO₂ surface due to adding of chromium impurities.