The effects of intermolecular interactions on the electric field gradients in ice and liquid water

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Abstract
Ab initio self-consistent field calculations of the electric field gradients (efg) at the nuclei in hydrogen bonded pentamers of H2O are reported, and the shifts relative to the isolated molecule discussed with reference to the importance of the electrostatic, polarization, exchange and charge transfer mechanisms. The results of electrostatic model calculations on ice structures in which a single H2O molecule as well as a hydrogen bonded pentamer (treated quantum mechanically) are surrounded by a point charge representation of the remaining molecules in the crystal lattice are also presented. The calculated efg shifts are compared with the observed solid state shifts in the nuclear quadrupole coupling constants for normal ice (Ih) and the high pressure polymorph ice VIII, assuming that the 17O and 2H nuclear quadrupole moments are -2·63 fm2 and 0·286 fm2 respectively. A new estimate of the 17O nuclear quadrupole coupling constant in liquid water is also proposed; this is χ(17O) = 8·5 ± 0·5 MHz.