J. Phys. IV France 08 (1998) Pr6-109-Pr6-113
Single particle dynamics of supercooled water and the kinetic glass transitionP. Gallo1, F. Sciortino1, P. Tartaglia1 and S.-H. Chen2
1 Dipartimento di Fisica and Istituto Nazionale per la Fisica della Materia, Università di Roma La Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
2 Department of Nuclear Engineering, Massachusetts Institute of Technology, 77 Massachusetts avenue, Cambridge MA 02139, U.S.A.
A molecular dynamics simulation in a time interval of 1 fs to 50 ns has been performed to study the single-particle dynamics of supercooled SPC/E water. In spite of the fact that, upon supercooling, SPC/E water progressively evolves into a more open structure locally, the single particle dynamics is shown to be dominated by the so called cage effect. The structural relaxation of the cage at low temperatures leads to the phenomenon of slow dynamics that can only be completely studied by following the trajectories into the ns range. Such results can be interpreted in the framework of the mode-coupling theory for supercooled liquids. The socalled critical Angell temperature of supercooled water can thus be interpreted as kinetic glas transition temperature. For this simulation various approximation previously used in literature for the evaluation of the intermediate scattering function from the experimental results are no longer valid. In fact upon supercooling the stochastic single-particle diffusion looses its validity and the diffusion process is then progressively controlled by the structural relaxation of the cage. The possibility of an experimental test of such a behaviour on real supercooled water is explored.
© EDP Sciences 1998