Density functional theory calculations have been performed on Ti-doped NaAlH4 clusters. First the electronic structure and stability of undoped clusters of different size and shape were studied, and then one of these clusters was chosen as a model system for a nano-sized NaAlH4 particle. A Ti atom added to the surface of this model preferably substituted a lattice Na near the surface, when using the NaAlH4 cluster with Ti adsorbed as the reference system and keeping the substituted atoms within the model. This may be a first step towards a model explaining the role of Ti during dehydrogenation and hydrogenation. (c) 2006 Elsevier B.V. All rights reserved.