Calculation of Electronic<i>g</i>-Tensors using Coupled Cluster Theory

A scheme for the calculation of the electronic g-tensor at the coupled cluster (CC) level is presented. The reported implementation employs an effective one-electron spin-orbit operator, allows the inclusion of arbitrary excitations in the cluster operator, and offers various options concerning the treatment of orbital relaxation and choice of reference determinants. In addition, the use of gauge-including atomic orbitals (GIAOs) is possible to overcome the gauge origin problem. Benchmark calculations for the NH ((3)Sigma(-)) radical reveal the importance of electron correlation effects for the accurate prediction of the g-shift as well as the slow basis set convergence of such calculations, which is only marginally improved by using GIAOs. CC singles and doubles results for the g-tensor are furthermore used to validate various functionals often used in density functional theory calculations. At least for radicals containing only light elements, the B3LYP hybrid functional appears to be the best among the four functionals tested in the present work.