Reorientation of OH-group connecting bifurcated H-bond acceptors in liquid water

The OH-group connecting bifurcated H-bond (HB) acceptors is one case of the three-centered HBs found in physical and biological systems. An example is the transition state of molecular reorientation jump mechanism in liquid water, ionic solutions, and hydration shells of biomolecules. In this Letter, the orientational time correlation functions of these special OH-groups in water were studied by performing molecular dynamics simulations and using the normal-mode approach developed recently. The reorientation angle of the OH-group before entering the diffusive regime can be estimated through the plateau in the mean-square rotational displacement calculated by several methods.