Dipole aggregation in rare-earth-doped fluorides, using the HADES code to calculate the energies of the defects was extensively studied. The binding energy values determined for dipoles and dimers agree quite well with published data. The possibility of creation of mixed dimers took into account the size of the impurities and also the electronic configuration. The results obtained confirmed that binding energies depend upon the ionic radius of the impurities and revealed a preferential order for the formation of mixed dimers. For the impurities with ionic radii larger than or very near to that for calcium the chance of forming mixed dimers is greater than for smaller impurities. The obtained values of the energies confirm the possibility of mixed dimer creation although simple dimers are preferentially formed first.