Ab initio QM/MM dynamics of anion-water hydrogen bonds in aqueous solution

Dynamical properties of F−-water and Cl−-water hydrogen bonds in aqueous solution have been studied by ab initio QM/MM molecular dynamics simulations, in which the whole first hydration sphere of the anion was treated at Hartree-Fock level using D95V+, 6-31+G and D95V++ basis sets for F−, Cl− and water, respectively. According to a detailed analysis of the bond distortions and shifts in the corresponding bending and stretching frequencies as well as the mean residence times of water molecules surrounding the ions, F− clearly acts as a 'structure-maker', while Cl− solvation leads to a more flexible structure with frequent re-arrangements of the hydrogen bonds.