Molecular dynamics behind the principle relaxation of water: Observation of inertia and memory effects*

We report an analysis of the single dipole to collective dipole moment time correlation function (TCF) calculated from the molecular dynamics simulations of liquid water at room temperature with a rigid and nonpolarizable TIP5P water model [1]. The single to collective dipole moment TCF is especially important because it allows us to investigate the local relaxation processes in a cluster of molecules and it can be directly related to the dielectric constant via the Fatuzzo-Mason equation. We have calculated the collective dipole moment associated with the first through fourth solvation shells and observed retarded relaxation processes for outer shells. We have also discovered a long-term and long-range rephasing process of about 40 ps involving more than 500 molecules. [1] M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000).