Nuclear magnetic resonance (NMR) shielding tensors for the oxygen and hydrogen nuclei, as well as nuclear quadrupole coupling tensors for the oxygen and deuterium nuclei of water in the liquid and gaseous state, are calculated using Hartree-Fock and density functional theory methods, for snapshots sampled from Car-Parrinello molecular dynamics trajectories. Clusters representing local liquid structures and instantaneous configurations of a single molecule representing low-density gas are fed into a quantum chemical program for the calculation of the NMR tensors. The average isotropic and anisotropic tensorial properties of 400 samples in both states, averaged using a common Eckart coordinate frame, are calculated from the data. We report results for the gas-to-liquid chemical shifts of (17)O and (1)H nuclei, as well as the corresponding change in the nuclear quadrupole couplings of (17)O and (2)H. Full thermally averaged shielding and quadrupole coupling tensors are reported for the gaseous and liquid-state water, for the first time in the case of liquid. Electron correlation effects, the difference of classical vs quantum mechanical rovibrational averaging, and different methods of averaging anisotropic properties are discussed.

Aqueous solutions of deuterated hydrofluoric acid (DF) have been studied at three concentrations using ab initio molecular dynamics (AIMD). At low concentration, DF was found to form a strongly bound complex, dynamically fluctuating between F−D···D2O and F-···D3O+ structures. The coordination number of molecular DF is as low as 2. The fluctuation behavior was observed also at higher concentrations, although in that case 40% of the DFs can be considered as dissociated into F- ions rather than being a part of F-···D3O+ complexes. No FDF- ions formed spontaenously at ambient temperature. One such complex was built, and it was stable for the whole simulation time (6 ps). The increasing acidity as a function of concentration is suggested to derive partly from the increasing stabilization of F- when its surroundings become more ionic. The F- ion can be also stabilized by HF molecule, which results in a bifluoride ion. The high DF concentration also lowers all coordination numbers and compresses the first solvation shell of heavy atoms (O and F), compared to low concentration or bulk water. Vibrational spectra obtained from the velocity autocorrelation functions agree with experimental results from spectroscopy. The increased intermolecular forces together with the weakening of the intramolecular ones can also be seen in the vibrational power spectra.

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