Ab initio QM/MM simulations of water and hydrated cations

An overview of the recent advances in ab initio simulations of liquid water and aqueous systems containing cations is given. In both cases a spherical region containing a central species (water molecule or ion, respectively) surrounded by a all nearest water molecules (coordination shell(s)) is treated quantum mechanically, i.e. at the Hartree-Fock level. Structural and dynamical insights are described by the O-O and M+-O (M=Metal) interactions, via the respective radial distribution functions and the velocity autocorrelation functions, respectively. This evaluation enables (i) the estimation of the number and the lifetime of the hydrogen bonds in liquid water, (ii) the definition of the hydration shell(s) of the cations, and (iii) the characterization of ions as either chaotropic or kosmotropic.