  Local polarization effects, induced by mono and divalent positive ions in
water, influence (and in turn are influenced by) the large scale structural
properties of the solvent. Experiments can only distinguish this process of
interplay in a generic qualitative way. Instead, first principles quantum
calculations can address the question at both electronic and atomistic scale,
accounting for electronic polarization as well as geometrical conformations.
For this reason we study the extension of the scales' interconnection by means
of first principle Car-Parrinello molecular dynamics applied to systems of
different size. In this way we identify the general aspects dominating the
physics of the first solvation shell and their connection to the effects
related to the formation of the outer shells and eventually the bulk. We show
that while the influence of the ions is extended to the first shell only, the
water-water interaction is instead playing a dominant role even within the
first shell independently from the size or the charge of the ion.
