Statistically Converged Properties of Water from Ab Initio Molecular Dynamics Simulations

We present results from an ab initio molecular dynamics study of pure water. Using the resources available at the HLRB2 we were able to produce the first trajectories of sufficient length and number, that allow to study dynamical processes on the picosecond timescale with statistically reliable results. Additionally we computed a statistically converged infrared absorption spectrum from 0–4000 cm−1, which is in good agreement with the experimental observation. In particular, at THz frequencies the spectra qualitatively reproduce important features, whereas, in contrast, force field based simulations have been shown to utterly fail. In order to compensate for the neglect of quantum effects for the nuclei in classical dynamics simulations on an ab initio potential energy surface and potential overbinding in conjunction with the used electron structure method, we applied an increased intrinsic temperature of 400K in order to obtain structural and dynamical properties corresponding to an experimental temperature of 300K.