Cluster geometries from density functional calculations - prospects and limitations

The use of density functional methods to calculate the structures and energ ies of clusters of atoms is discussed. Applications to phosphorus and sulph ur show that unexpected structures occur even in small clusters. Calculatio ns of many isomers of carbon clusters from C-4 to C-32 (n even) show striki ng results, with periodic patterns in several structural classes. Gradient corrections are significant, but regular within a given cluster type. Some strengths and limitations of the approach are discussed.