Memory function models for the diffusive dynamics of supercooled water studied by QENS and molecular dynamics simulations

摘要

A second memory function model has been applied to the analysis of the incoherent neutron quasi-elastic scattering of pure H_2O in the normal and supercooled regime. Such model has already been applied by us to the description of the single-particle dynamics obtained from molecular dynamics simulations on water. The model takes into account two characteristic relaxation times, #tau#_1 and #tau#_2, which can be related to hindered motions of the water protons within the nearest-neighbour cage and to the relaxation of water clusters, respectively. The momentum, Q, and the temperature dependence of #tau#_1 and #tau#_2 have been derived. #tau#_1 varies almost linearly with Q and, in the supercooled region, it increases with decreasing temperature. #tau#_2, which gives only a small contribution to the total memory function, stays nearly constant above approx 1 A~(-1), below this value it tends to increase both with decreasing temperature and Q.