The structure of the stoichiometric and reduced SnO2(110) surface

Abstract

First-principles calculations based on density functional theory (DFT) and the pseudopotential method have been used to study the stoichiometric and reduced SnO 2 (110) surface. The ionic relaxations are found to be moderate for both the stoichiometric and reduced surfaces, and are very similar to those found in recent DFT-pseudopotential work on TiO 2 . Removal of neutral oxygen leaves two electrons per oxygen on the surface, which are distributed in channels passing through bridging oxygen sites. The associated electron density can be attributed to reduction of tin from Sn 4+ to Sn 2+ , but only if the charge distribution on Sn 2+ is recognized to be highly asymmetric. Reduction of the surface gives rise to a broad distribution of gap states, in qualitative agreement with spectroscopic measurements.

The adsorption of H2O on TiO2 and SnO2(110) studied by first-principles calculations

“…means that there is an appreciable overlap of the oxygen and metal core spheres in the SnO 2 and TiO 2 crystals, and in principle this could cause inaccuracies. However, direct comparisons of the present results with our earlier work on SnO 2 [25], which employed an oxygen pseudopotential with the smaller core radius of 1.25 a.u., show that any errors due to core overlap are very small.…”

“…The width we use corresponds to two O -M 2 O 2 -O units, and is such that planes of bridging oxygens on the surfaces facing each other across the vacuum are separated by about 6.8Å. This vacuum width is somewhat greater then was used in our earlier calculations on SnO 2 (110) [25]. (It will be convenient in the following to specify slab thickness and vacuum width in terms of the equivalent width of O -M 2 O 2 -O units.…”

“…For presentation purposes, we have broadened the calculated DOS and LDOS by Gaussians of width 0.5 eV. In the ground state calculations the Brillouin zone sampling is performed using the lowest order Monkhorst-Pack set of k points [54], as in our previous work on SnO 2 [24,25].…”

“…This approach has been widely used for oxides, including MgO [19] [24], and is known to give accurate results for the energetics of perfect crystals, lattice defects, surfaces and molecular adsorption. We have recently reported a detailed study of the stoichiometric and reduced SnO 2 (110) surface using this approach [25]. However, since the energetics of dissociation is not generally described very accurately within the standard local density approximation (LDA), we include gradient corrections in the present work, using the Becke-Perdew scheme [26,27].…”

First-principles spin-polarized calculations on the reduced and reconstructedTiO2(110) surface

“…Scientifically this is challenging, and our understanding of oxide surfaces lags well behind that of other materials: 1 experimental studies of oxide surfaces are much more difficult than those of metals and semiconductors, and theory has, until quite recently, relied upon insights from simple interaction models. However, first-principles simulations, in which the electrons are treated quantum mechanically, are now being used to make very significant contributions to the understanding of oxide surfaces, for example, in MgO, 2 Al 2 O 3 , 3 SnO 2 , 4 and TiO 2 . [5][6][7][8][9][10][11] Our aim in the present paper is to use first-principles simulations to investigate the stoichiometric and reduced ͑110͒ surface of TiO 2 .…”