Density functional calculation of the electric field gradient in cadmium complexes: Comparison with Hartree-Fock, second-order Moller-Plesset, and experimental results

Density functional B3LYP calculations of the electric field gradient at the metal site in small linear cadmium model complexes and two larger structures are presented. The results are compared to those by Hartree-Fock, second-order Moller-Plesset, and experiment. The quality of the cadmium basis set is tested by augmenting the uncontracted basis set of Kello and Sadlej with additional basis functions. B3LYP generally gives an electric field gradient which is smaller in magnitude than Hartree-Fock with a reduction of the electric field gradient in the range 0.1-1.4 atomic units (au) or 15-30% for the examined complexes. This reduction of the electric field gradient seems to be caused by a larger cancellation of p- and d-contributions from the Cd atomic orbitals than for the other methods. The second-order Moller-Plesset result for the electric field gradient lies between B3LYP and Hartree-Fock, except for the complex chloroglycylglycinato(imidazole)-cadmium. The changes of the electric field gradient between tested basis sets are up to 0.2 au or 6% and smaller than the variations between different methods. The addition of tight functions to the cadmium basis set has a smaller effect than extra basis functions in the range already spanned. Comparing to experiment, B3LYP gives the best result for dimethylcadmium. For the two larger cadmium complexes Hartree-Fock and second-order Moller-Plesset are closer to the measured values, but crystal effects are neglected making the comparison with experiment more uncertain than for dimethylcadmium.