Structures of clusters (Cu2Se)(n) and (Cu2Se)(n)(PR(3))(m) for n less than or equal to 6 and R = H, CH3 are presented which have been determined in ab initio calculations including dynamical electron correlation (Moller-Plesset perturbation theory and coupled cluster). Various stable isomers exist for the dimer and larger clusters. The energetic separation of the isomers is rather small, and the energy hypersurfaces are in part very shallow. A few basic structural criteria deduced from the small cluster structures turned out to be ideally fulfilled in the hexamer Cu12Se6 already known experimentally as a Ligand-stabilized species. The bonding of phosphine ligands affects the cluster structures significantly only in cases where an ideal coordination at Cu conflicts with steric requirements. Bonding energies per monomer unit of ligand-free clusters and CuP bonding energies suggest that the clusters are energetically unstable.