Diffusion effects of hydrogen bond fluctuations. I. The long time regime of the translational and rotational diffusion of water

A theoretical scheme to evaluate the long‐time effects of hydrogen bond fluctuations on water dynamics is carefully reexamined in the light of recent experimental results of quasi-elastic neutron scattering (QENS). A molecular dynamics computer simulation is also carried out on a fairly large (343 TIP4P molecules) sample and for a total time of ≈100 ps. at three temperatures. The length of the runs has allowed to obtain good results for a number of properties. Also the temperature dependence of the static dielectric constant agrees with the experimental data. Further, some crucial predictions of our theoretical model have been carefully checked. The prediction on the deviation from Fick’s law is found to be in a satisfactory accord with the results of our computer simulation. The reasons for the less satisfactory agreement with the low‐temperature results of QENS are discussed.