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The use of molecular dynamics simulations with ab initio SCF calculations for the determination of the oxygen-17 quadrupole coupling constant in liquid water

Molecular dynamics simulations for H2 17O were performed with two different potentials from the literature. After equilibration, snapshots were taken at intervals and the configurations thereby obtained used to randomly select clusters of molecules. For the central oxygen of these clusters the electric field gradient was then calculated with standard ab initio self-consistent field (SCF) calculations. The field gradients were converted to quadrupole couplings with a factor obtained previously in gas phase calculations and averaged to obtain the 17O coupling in liquid water. At 300 K a best estimate of 8·9 ± 0·3 MHz for the coupling constant and 0·72 ± 0·04 for η were found. The coupling constant at 360 K is about 0·1 MHz larger but the temperature dependence is not significant.