Structural Origin of Translational Jumps and Allied Dynamical Anomalies in Supercooled Water

The microscopic origin of dynamical anomalies in supercooled water remains a long-standing puzzle. Using extensive molecular dynamics simulations and the translational jump-diffusion (TJD) formalism, we reveal that these anomalies originate from rare but crucial translational jumps, which are large-amplitude displacements of water molecules. We discover a distinct structural mechanism for jump initiation, characterized by a coherent sequence of local fluctuations: loss of tetrahedral order, weakening of hydrogen bonds, and a "push-pull solvation" effect marked by the expansion of the first and compression of the second solvation shell. At deeply supercooled temperatures, long-range spatial correlations amplify this collective push-pull effect, leading to a dominant jump contribution to diffusion. Our results establish a direct link between local structural fluctuations and macroscopic transport anomalies, offering a unified microscopic basis for the breakdown of classical transport laws in supercooled water.