NUCLEAR MAGNETIC SHIELDING CONSTANTS IN THE CC2 MODEL

Test calculations of nuclear magnetic shielding constants in the CC2 m odel are performed using the gauge-including atomic orbital approach. Absolute shielding constants are reported for representative first-row hydrides, a few multiply bonded molecules and some challenging cases, The performance of CC2 is analyzed by comparison with experimental da ta and results from calculations employing more sophisticated treatmen ts of electron correlation. In most cases, CC2 shieldings and chemical shifts are close to those obtained at second-order perturbation theor y, despite the fact that the CC2 model includes an approximate treatme nt of orbital relaxation effects at the correlated level. (C) 1997 Pub lished by Elsevier Science B.V.