NMR chemical shifts of ice and liquid water: The effects of condensation

We report the results of ab Initio density functional theory calculations o f the NMR chemical shift of liquid water and hexagonal ice. Depending on th e structural model used, the calculated isotropic shift of ice Ih with resp ect to the gas phase is -8.0 +/- 0.2 or -8.1 +/- 0.1 ppm for the proton, an d -48.6 +/- 0.02 or -48.1 +/- 0.02 ppm for oxygen. The proton anisotropy is -33.4 +/- 0.2 or -33.6 +/- 0.2 ppm. Using snapshots from ab initio molecul ar dynamics simulations, we find a gas-to-liquid shift of -5.8 +/- 0.1 ppm for hydrogen, and -36.6 +/- 0.5 ppm for oxygen. Molecules beyond the first solvation shell influence the proton chemical shift predominantly via the e lectric field generated by their permanent electric dipole moment. Finally, we show that it is possible to reproduce the proton chemical shifts in the condensed phases by an empirical function of the local molecular geometry.