Benchmark calculations of the shielding constants in the water dimer

The NMR shielding constants in (H2O)2 have been calculated using GIAO-SCF, MP2, MP4 and CCSD methods and for a range of basis sets. According to the obtained results the 6-311++G** or aug-cc-pVDZ basis sets are recommended for SCF calculations, and the aug-cc-pVXZ series is suggested for correlated calculations of the interaction-induced changes in the shielding constants. The counterpoise correction improves the results towards the basis set limit and is essential in the case of 17O shielding. Correlation effects are substantial for the changes in 17O shielding, less so for 1H shielding. They are overestimated by the MP2 method.