Accurate prediction of nuclear magnetic resonance shielding constants: towards the accuracy of CCSD(T) complete basis set limit.

In this work, we have calculated the nuclear magnetic resonance (NMR) shielding constants for 42 molecules at the levels of second order Mo̸ller-Plesset perturbation (MP2) and coupled-cluster singles and doubles model augmented by perturbative corrections for triple excitations CCSD(T). Basis set extrapolations to the complete basis set (CBS) limit have been performed. A focal-point analysis method for magnetic parameters was proposed here, which adds the [σ(e)(CCSD(T)) - σ(e)(MP2)] difference to the MP2∕CBS number to approximate the corresponding CCSD(T)∕CBS value. Systematical comparison has demonstrated the usefulness of this FPA-M∕CBS scheme.