title: Raman Spectra of Liquid Water from Ab Initio Molecular Dynamics: Vibrational Signatures of Charge Fluctuations in the Hydrogen Bond Network.
abstract: We report the first ab initio simulations of the Raman spectra of liquid water, obtained by combining first principles molecular dynamics and density functional perturbation theory. Our computed spectra are in good agreement with experiments, especially in the low frequency region. We also describe a systematic strategy to analyze the Raman intensities, which is of general applicability to molecular solids and liquids, and it is based on maximally localized Wannier functions and effective molecular polarizabilities. Our analysis revealed the presence of intermolecular charge fluctuations accompanying the hydrogen bond (HB) stretching modes at 270 cm(-1), in spite of the absence of any Raman activity in the isotropic spectrum. We also found that charge fluctuations partly contribute to the 200 cm(-1) peak in the anisotropic spectrum, thus providing insight into the controversial origin of such peak. Our results highlighted the importance of taking into account electronic effects in interpreting the Raman spectra of liquid water and the key role of charge fluctuations within the HB network; they also pointed at the inaccuracies of models using constant molecular polarizabilities to describe the Raman response of liquid water.
authors.affiliation: Department of Chemistry, University of California , Davis, California 95616, United States.
authors.forename: Quan
authors.initials: Q
authors.lastname: Wan
authors.affiliation: Department of Chemistry, University of California , Davis, California 95616, United States.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Spanu
authors.affiliation: Department of Chemistry, University of California , Davis, California 95616, United States.|Department of Physics, University of California , Davis, California 95616, United States, and.
authors.forename: Giulia A
authors.initials: GA
authors.lastname: Galli
authors.affiliation: Department of Computer Science, University of California , Davis, California 95616, United States.
authors.forename: François
authors.initials: F
authors.lastname: Gygi