Reconstructions of strongly reduced SnO2(110) studied by first-principles methods

First-principles calculations based on density-functional theory and pseudopotentials are used to study the energetics and structure of highly reduced SnO2(110) surfaces for which detailed experimental data have recently been reported. In the surfaces studied, all bridging oxygen ions are absent, and in-plane vacancies are present, the mean number of these vacancies per surface unit cell being theta = 0.5 or more. By comparing the calculated energies of competing vacancy orderings at 0 = 0.5, we find that the most stable has (4 x 1) symmetry; this is the model proposed earlier for the (4 x 1) reconstruction observed by LEED and STM measurements. However, our calculated relaxed structure disagrees with that deduced from LEED measurements. Our calculated STM images for this structure also suggest the need for a reinterpretation of the experimental results. A model proposed for the (2 x 1) reconstruction recently found to coexist with the (I x 1) reconstruction is also studied, and our calculations appear to be inconsistent with the model. (C) 2002 Elsevier Science B.V. All rights reserved.