Basis-set convergence of nuclear magnetic shielding constants in molecular HF and MP2 calculations

Recently, segmented contracted basis sets of double, triple, quadruple and quintuple zeta valence quality plus polarization functions (XZP, X = D, T, Q and 5) for the atoms from H to Ar were presented by Jorge et al. We report a systematic study of basis sets required to obtain accurate values for nuclear magnetic shielding tensors for 20 molecules at their experimental equilibrium geometries. Two methods were examined: Hartree-Fock (HF) and second-order Moller-Plesset perturbation theory (MP2). Gauge-invariant atomic orbitals were used to guarantee origin-independent values of magnetic properties. By direct calculations or by fitting the directly calculated values through two extrapolation schemes, estimates of the HF and MP2 complete basis-set limit have been obtained. Comparison with experiment and benchmark results reported in the literature is made.