Correlation effects on the structure and dynamics of the H3O+hydrate: B3LYP/MM and MP2/MM MD simulations

Abstract

Two combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations, namely B3LYP/MM and MP2/MM, have been performed to investigate the possible influence of electron correlation on the structure and dynamics of the H₃O⁺ hydrate. In comparison to the previously published HF/MM results, both B3LYP/MM and MP2/MM simulations clearly reveal stronger H₃O⁺–water hydrogen bond interactions, which are reflected in a slightly greater compactness of the H₃O⁺ hydrate. However, the B3LYP/MM simulation, although providing structural details very close to the MP2/MM data, shows an artificially slow dynamic nature of some first shell water molecules as a consequence of the formation of a long-lived H₃O⁺⋯H₂O hydrogen bonding structure.