The composition and thermodynamic stability of the (110) surface of Sn(1) (-) (x)Ti(x)O(2) rutile solid solutions was investigated as a function of Ti-distribution and content up to the formation of a full TiO(2) surface monolayer. The bulk and (110) surface properties of Sn(1) (-) (x)Ti(x)O(2) were compared to that of the pure SnO(2) and TiO(2) crystal. A large supercell of 720 atoms and a localized basis set based on the Gaussian and plane wave scheme allowed the investigation of very low Ti-content and symmetry. For the bulk, optimization of the crystal structure confirmed that up to a Ti-content of 3.3 at.%, the lattice parameters (a, c) of SnO(2) do not change. Increasing further the Ti-content decreased both lattice parameters down to those of TiO(2). The surface energy of these solid solutions did not change for Ti-substitution in the bulk of up to 20 at.%. In contrast, substitution in the surface layer rapidly decreased the surface energy from 0.99 to 0.74 J/m(2) with increasing Ti-content from 0 to 20 at.%. As a result, systems with Ti atoms distributed in the surface (surface enrichment) had always lower energies and thus were thermodynamically more favorable than those with Ti homogeneously distributed in the bulk. This was attributed to the lower energy necessary to break the Ti - O bonds than Sn - O bonds in the surface layer. In fact, distributing the Ti atoms homogeneously or segregated in the (110) surface led to the same surface energy indicating that restructuring of the surface bond lengths has minimal impact on thermodynamic stability of these rutile systems. As a result, a first theoretical prediction of the composition of Sn(1) (-) (x)Ti(x)O(2) solid solutions is proposed. (C) 2011 Elsevier B.V. All rights reserved.