PROTON DYNAMICS IN SUPERCOOLED WATER BY MOLECULAR-DYNAMICS SIMULATIONS AND QUASI-ELASTIC NEUTRON-SCATTERING

A detailed study of the single-particle dynamics of liquid water in no rmal and supercooled regime has been carried out by comparing molecula r dynamics (MD) simulation results with now available high resolution quasielastic neutron scattering (PENS) data, Simulation runs have been performed at 264, 280, 292, and 305 K, using the extended simple poin t charge model, well suited for reproducing single-particle properties of H2O. The microscopic dynamics has been probed over a wide range of times and distances. The MD results indicate that a substantial coupl ing between translational and rotational dynamics exists already at ab out 1 ps. The decay of the translational dynamic correlations has been phenomenologically analyzed in terms of three exponential components, and the agreement between the parameters thus obtained from experimen tal and simulation derived datasets is quite satisfactory. Both QENS a nd MD data can not be described with sufficient accuracy by simple dif fusion models over the entire range of examined wave vectors. (C) 1996 American Institute of Physics.