DFT study of bare and dye-sensitized TiO2 clusters and nanocrystals

Structural and electronic properties of bare and dye-sensitized TiO2 clusters and nanoparticles with sizes of <= 2 nm have been studied by density functional theory (DFT) calculations. Starting from truncated bulk lattice structures, the degree of structural reorganization, including the formation of Ti=O surface species, of bare TiO2 anatase nanocrystals, is found to be sensitive to the quality of the computational method. The electronic structures of optimized 1-2 nm nanoparticles show well-developed band structures with essentially no electronic bandgap defect states. Significant bandgap broadening due to quantum size effects is observed as the size of the nanocrystals is reduced from 2 nm to 1 nm in diameter, but further bandgap widening is limited by increasingly severe competing surface defect sites as the particles become smaller than similar to 1 nm in diameter. The applicability of the TiO2 nanocrystals in modeling the electronic structure and electronic coupling at dye-sensitized TiO2 nanocrystal interfaces has been investigated by attachment of pyridine to one of the nanoparticle models via phosphonic or carboxylic acid anchor groups. (c) 2006 Wiley Periodicals, Inc.