Hartree-Fock (RHF) and second-order Møller-Plesset (MP2) first principles calculations have been performed to study the structures, stabilities, harmonic vibrational frequencies, and bonding properties of MgF 2 dimers and trimers, complementing our previous work (J. Phys. Chem. 2001, 105, 4126) on the MgF 2 monomer. The less energetic isomers found for (MgF 2) 2 and (MgF 2) 3 are the bridged F-(Mg 2 F 2)-F (D 2h) and F-MgF 2 -MgF 2 Mg-F (D 2d) structures, respectively. A new C s trimer structure has been found and characterized. Correlation energy corrections increase the Mg-F distances by 1.2-1.4% and do not modify appreciably the Mg-F-Mg and F-Mg-F angles. The dissociation energy per MgF 2 unit (DE) of (MgF 2) n increases with n. MP2 frequencies for the (MgF 2) 2 D 2h isomer are around 1.0% lower than their RHF equivalents. The whole set of computed frequencies for (MgF 2) n has allowed us to perform a critical analysis of the experimental vibrational data, where some spectral assignments remained uncertain. The atoms in molecules analysis of the electron density reveals that (MgF 2) n clusters are highly ionic, with almost nominal net atomic charges (q Mg = +1.8|e| and q F = -0.9|e|). Our previous polarizable-ions model accounts fairly well for the properties of these clusters, rationalizing the energy ordering of trimers in a physically sound way.