An ab initio molecular dynamics study of the frequency dependence of rotational motion in liquid water

We present a first principles calculation of the frequency dependence of rotational motion of OD bonds of deuterated water molecules in the liquid phase by means of ab initio molecular dynamics simulations. The fluctuating frequencies of the OD bonds are calculated through a time series analysis of the simulated trajectories and the frequency-resolved rotational dynamics are investigated in terms of the first and second-rank rotational correlation functions of the OD bond vectors. It is found that the short-time dynamics can depend significantly on the frequency which, in turn, is related to different hydrogen bonding environments, whereas the long-time dynamics is essentially frequency independent. A comparison of the current theoretical results with the recent polarization-resolved time dependent infrared spectroscopic results is also presented. (C) 2008 Elsevier B.V. All rights reserved.