  Recent experiments (F.H.J. Van Der Heyden et al., PRL 96, 224502 (2006)) of
streaming currents in silica nanochannels with divalent ions report charge
inversion, i.e. interfacial charges attracting counterions in excess of their
own nominal charge, in conflict with existing theoretical and simulation
results. We reveal the mechanism of charge inversion by using all-atomic
molecular dynamics simulations. Our results show excellent agreement with
experiments, both qualitatively and quantitatively. We further discuss the
implications of our study for the general problem of ionic correlations in
solutions as well as in regards of the properties of silica-water interfaces.
