Static and dynamic quantum effects in molecular liquids: a linearized path integral description of water

Structure, transport properties, and IR spectra including quantum effects are calculated for a flexible simple point charge model of liquid water. A recently introduced combination of a variational local harmonic description of the liquid potential surface and the classical Wigner approximation for the dynamics is used. The potential energy and interatomic radial distribution functions are in good agreement with accurate results from the literature and are significantly closer to experiment than predictions found from classical theory. The oxygen and hydrogen velocity correlation functions are also calculated, and the corresponding molecular diffusion coefficient is in good accord with existing theoretical estimates including quantum effects. Of most interest, an ab initio quantum correction factor is obtained to correct the far IR spectrum of water. When corrected, a spectrum based on a classical simulation yields results that agree well with experiment. Combined with internal tests of consistency, these observations indicate that this quite flexible approach will be effective for a variety of molecular problems involving the dynamics of light nuclei.