Slow dynamics in a model and real supercooled water

We made a molecular dynamics study of single-particle dynamics of water molecules in deeply supercooled liquid states. We find that the time evolution of various single-particle time correlation functions is characterized by a fast initial relaxation toward a plateau region, where it shows a self-similar dynamics, then followed by a slow, stretched exponential decay to zero at much later times. We interpret these results in the frame-work of a mode-coupling theory for supercooled liquids. We relate the apparent anomalies of transport coefficients in this model water, on lowering the temperature, to the formation of a long-lived cage around each water molecule and the associated slow dynamics of the cages. The experimentally observed so-called Angell temperature, which is an apparent limit of supercooling in liquid water, could thus be interpreted as a kinetic glass transition temperature predicted by the mode-coupling theory. We then discuss to what extent the experimental incoherent quasi-elastic neutron scattering data from supercooled bulk water support the idea of the existence of the slow dynamics.