The electronic and geometrical structures of (GaAS)(n)Mn-m and (GaAS)(n)Fe-m clusters (for m = 1, n = 2-4, for m = 2, n = 1-4, and for m = 3. n = 4) are studied using density functional theory with generalized gradient approximation. The clusters are found to possess a large number of isomers that are close in total energy. For the clusters with multiple metal atoms, the ferromagnetic and antiferromagnetic couplings of the excess spin densities at the metal sites are close in energy. (GaAs)(2)Mn-2, (GaAs)(3)Mn-2, and (GaAs)(4)Mn-3 have antiferromagnetic ground states, while all of the Fe-n-containing species, GaAsMn2 and (GaAs)(4)Mn-2 have ferromagnetic ground states. (c) 2007 Elsevier B.V. All rights reserved.