Lowest-energy structures of (WO3)n (2 ≤ n ≤ 12) clusters from first-principles global search

Using genetic algorithm combined with density functional theory calculations, we performed global search for the most stable structures of (WO3)n clusters for n = 2–12. Small (WO3)n clusters with n = 3 or 4 adopt ring-like configurations with W–O alternating arrangement. Starting from (WO3)8, the tungsten oxide clusters transform to symmetric spherical-like cages. The relative stability, HOMO–LUMO gap, electronic states of these (WO3)n clusters were discussed. Analysis of wavefunctions of frontier orbitals and electron density of states shows that the valence bands are dominated by the 2p electrons from oxygen and the conduction bands are mainly contributed by the 5d states from tungsten.