THE USE OF MOLECULAR-DYNAMICS SIMULATIONS WITH AB-INITIO SCF CALCULATIONS FOR THE DETERMINATION OF THE O-17 QUADRUPOLE COUPLING-CONSTANT IN LIQUID WATER

Molecular dynamics simulations for (H2O)-O-17 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 O-17 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 eta were found. The coupling constant at 360K is about 0.1 MHz larger but the temperature dependence is not significant.