The hydration shell structure of Li+ investigated by Born-Oppenheimer ab initio QM/MM dynamics

A combined ab initio quantum mechanical (QM) and molecular mechanical (MM) molecular dynamics simulation has been applied to study the non-additive contributions to the surroundings of Li+ in water. The first hydration sphere of Li+ is treated by Born-Oppenheimer ab initio quantum mechanics, while the rest is described by classical pair potentials. A tetrahedral structure of four water molecules in the first solvation shell of Li+ is found by this combined QM/MM method with a valence double-zeta basis set, in contrast to the octahedral structure obtained by the traditional simulation using pair potentials. (C) 1998 Elsevier Science B.V.