Correlated and gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach

We report for the first time an extended series of correlated origin independent calculations of nuclear magnetic shielding tensors using the approach of continuous transformation of the origin of the current density to annihilate its diamagnetic contribution. A systematic study was undertaken to develop optimal basis sets for H, C, N, O, F correlated nuclear magnetic shieldings, looking for the best compromise between accuracy and size. Beyond Hartree-Fock calculations were carried out at two levels of accuracy, the multiconfigurational self-consistent field based on the complete active space scheme, and the second-order polarization propagator approximation (SOPPA). In addition we present the first shielding calculations employing the second-order polarization propagator approximation with coupled cluster singles and doubles amplitudes SOPPA (CCSD). (C) 2003 American Institute of Physics.