Small tin oxide grains: structural and electronic properties evaluated using the density functional theory

This study is motivated by the complex properties of tin oxides and by the lack of detailed theoretical information on the clustered state of these materials. Therefore small grains of a columnar and a spherical shape with a rutile lattice and a size up to 100 atoms have been considered and their structural and electronic properties evaluated using the density functional theory. The calculations show that the rutile skeleton is retained starting from a size of 20 atoms and the absence of reconstruction is particularly evident in the spherical grains. However, reconstruction also occurs and the physical force behind it is an increase in the coordination among tin-oxygen and oxygen oxygen atoms. The binding energy has a primary dependence on the grain size, whereas only marginal effects arise from the grain structure. The density of states has bands below and above the Fermi levels which are not observed in the crystalline material and are therefore peculiar to the clustered state.