| Abstract
| - The effect of the nanostructure on the photochemistry of TiO2 is an active field of research owing to itsapplications in photocatalysis and photovoltaics. Despite this interest, little is known of the structure of smallparticles of this oxide with sizes at the nanometer length scale. Here we present a computational study thatlocates the global minima in the potential energy surface of TinO2n clusters with n = 1−15. The searchprocedure does not refer to any of the known TiO2 polymorphs, and is based on a novel combination ofsimulated annealing and Monte Carlo basin hopping simulations, together with genetic algorithm techniques,with the energy calculated by means of an interatomic potential. The application of several different methodsincreases our confidence of having located the global minimum. The stable structures are then refined bymeans of density functional theory calculations. The results from the two techniques are similar, although themethods based on interatomic potentials are unable to describe some subtle effects. The agreement is especiallygood for the larger particles, with n = 9−15. For these sizes the structures are compact, with a preference fora central octahedron and a surrounding layer of 4- and 5-fold coordinated Ti atoms, although there seems tobe some energy penalty for particles containing the 5-fold coordinated metal atoms with square base pyramidgeometry and dangling TiO bonds. The novel structures reported provide the basis for further computationalstudies of the effect of nanostructure on adsorption, photochemistry, and nucleation of this material.
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