The lowest-energy structures were obtained for GanNn clusters (n = 4-12) using gradient-corrected density functional theory. For each cluster size, a number of structural isomers were constructed and optimized. Crossover from ring to cage-like structures were found at Ga8N8. The observed cage-like configurations consisting of six-membered rings with gallium-nitrogen alternative arrangement can be viewed as embryo of wurtzite structure of gallium nitride crystal. The size-dependence of cluster properties such as binding energy, HOMO-LUMO gaps, ionization potentials, electron affinities, and Mulliken charges have been computed and analyzed. The bonding characteristics of the GanNn clusters were discussed. (c) 2006 Elsevier B.V. All rights reserved.