On the calculations of the nuclear shielding constants in small water clusters

The comparative study of the calculated ab initio 17O and 1H shielding constants for water clusters (H2O)n, n = 2-6, 12 and 17, is presented. The comparison of different methods and the convergence of a basis set size were analyzed to enable the choice of the most efficient method of calculations. DFT(B3LYP)/aug-cc-pCVDZ calculations of shielding constants were performed for all clusters under the study. The correlation of the changes in the 1H shielding constants on intra- and intermolecular distances was observed. The changes of the 17O shielding constants depend strongly on the cluster size and its hydrogen-bonding topology. The largest shift (−76.2 ppm) was found for the central oxygen atom surrounded by two hydration shells in the largest water cluster, (H2O)17. The interaction-induced changes in the 17O shielding constants are found to be non-additive.