The nucleation of small Cu clusters at the surface of SiO2 has been investigated by means of ab initio quantum chemical calculations using cluster models. The interaction of Cu, clusters (n = 1-5) with a nonbridging oxygen, NBO, a paramagnetic point defect of silica, has been studied by means of DFT calculations using the B3LYP exchange-correlation potential. Different from the regular nondefective surface, characterized by a weak adhesion with metal species, strong metal-oxide interface bonds form at the NBO centers. The Cu clusters are bound with one or two Cu atoms with the NBO forming covalent polar bonds. The partial charge transfer to the oxide favors the formation of electrostatic interactions between the metal cluster and the two-coordinated O atoms of the silica surface. Some observable consequences of the cluster nucleation have been studied, including: core level shifts and the appearance of new states in the gap of the oxide.