Nuclear magnetic shieldings in solution: Gauge invariant atomic orbital calculation using the polarizable continuum model

We present the gauge invariant atomic orbital (GIAO) calculation of nuclear magnetic shieldings for solvated molecules described within the polarizabl e continuum model (PCM). The performance of the PCM-GIAO approach is tested in a benchmark calculation of isotropic C-13, N-15, and O-17 shielding con stants for CH3CN and CH3NO2 in vacuo and in water, both at the Hartree-Fock and density functional levels of theory. Various aspects of the calculatio n of solvent effects on these properties, such as the dependence on the bas is set, the electron correlation, and the size of the molecular cavity embe dding the solute, are taken into account and discussed. An interpretation o f the gas-to-solution shielding variations in terms of a combined action of the solvent reaction field and the shielding polarizabilities is also give n. (C) 1999 American Institute of Physics. [S0021-9606(99)30115-X].